Obrazy na stronie
PDF
ePub
[ocr errors]

the same thread dangle, and you have fish with a miniature grey-hound's the legs; split the tip of the thread head; it is the pipe-fish, Syngnainto three filaments, and you have thus anguineus. Pop him in; also the head; gum bits of dirty wool, this bit of red weed, on which I obabout as large as a pin's head, on the serve some Polyzoa clustering. What second legs, and you have the egg- is this? a tiny Daisy on a frond of sacs: and with this the animal is weed ? the beauty! No, now it is in complete. The microscope reveals the bottle, it turns out to be an Eolis, fresh wonders, the head being fur- Eolis alba, lovely among the lovelinished with crablike nippers; the est. Stay! here are two cowries, and alimentary tube, instead of occupying alive! The shells every one has seen, an isolated and dignified position in but few of us have seen the animals; the body, meanders out into each of so the capture is very welcome. My the legs, so that the leg repeats the back is aching with all this stooping body in its internal structure, as well and groping, and I really must get as in aspect. This ramified aliment- home now, content with my day's ary canal is covered with brownish- work. One farewell glance in at that yellow globules or cells, called “he- pool, and I have done. Lying on patic cells," upon no very convincing my face, and dangling my feet in evidence, and supposed to represent a water, I peer scrutinisingly for some rudimentary liver. Mr. Gosse, in his minutes, and bear off a lovely green pleasant book on Tenby, mistakes Actæon, as a reward. Now I will this intestine for the circulating sys- turn homewards. tem; but the animal has no circulat- Another day, in idler mood, we ing system whatever." Each of the ramble along the shore in receipt of long and many-jointed limbs is per- windfalls. A bottle is always ready forated by a central vessel,” he says, in the pocket, and something is cer“ the walls of which contract periodi- tain to turn up. The stem and root of cally with a pulsation exactly resem- that oar-weed, for example, is worth bling that of a heart, by which gran- an investigating glance, certain as it ules or pellucid corpuscles of some is of being a colony of life. The sort or other are forced forward." It tiny annelids, white, green, and red, was food which Mr. Gosse saw thus wriggle in and out among the shelmoved; the blood-circulation, such tering shadows of these roots; the as it is, he correctly saw in what he sponges and polyzoa cluster on them; describes as the extra-vascular cir- and see! what pink-and-white feathery culation; only we should add, that creature is this, clasping the weed cascular circulation there is none. with a circle of pale pink roots ? By The blood, if blood it can be called, heavens! it is a Comatula," the rois outside the intestine, bathing the mance of the sea ;" and now that it walls of the body, and moved to and feels the grateful sea-water again, fro by the peristaltic action of the in- how it expands its feathers, and retestine. Curious, as this Nymphon veals itself as an animal fern, margracile is, I had reason to be the vellous to look upon. Sudden joy more pleased at finding one, because leaps in our hearts at the sight of while the latest authorities declare this creature, hitherto known only nothing to be known of the develop- from hazy descriptions and inadement of the Pycnogonidae, I had been quate engravings. There is interest fortunate enough at Ilfracombe, to in reading about Crinoidea, fossil and discover some of the embryonic recent, and in learning that the phases, of which I made drawings, Comatula is one of these, having and awaited further opportunity for kindred with star-fishes; but how pursuing the subject.

that interest is intensified by direct Here, in a pool, we find three curi- inspection of the living animal! I ous fish, one a ribbon-fish, the her ould not satiate myself with looking two unknown to me; and on raising at my prize.* All the way home the the stone, behold, a queer eel-like bottle was constantly being raised to

* I have since had several, but utterly inferior in colour and grace to this the first I ever saw.

my loving regard, that I might feast which produced no Astronomy in myself upon the waving grace of centuries of watching. They find those pink and white feathers; and their place in science, only as the I thought of the poetical passage in architectural mind disposes them in which Edward Forbes expressed his due co-ordination. Wbat should we emotions about these Crinoidea which think of a chemist who, on mere in “raise up a vision of an early world, spection of substances, unaided by a world the potentates of wbich were re-agents, and his balance, hoped to not men, but animals—of seas on further Chemistry? What would lists whose tranquil surfaces myriads of of such observations avail? And in convoluted Nautili sported, and in the far more complex science of whose depths millions of Lily-stars Biology, how shall cursory inspeo waved wilfully on their slender stems. tion, superficial observation, avail? Now, the Lily-stars and Nautili are We must follow the Methods which almost gone; a few lovely stragglers have led to certainty in the exact of those once abounding tribes re- sciences. We must render the commain to evidence the wondrous forms plex facts of Life as siipple as we and structures of their comrades. can, by processes of elimination. ExOther beings, not less wonderful, and periment must go band in hand with scarcely less graceful, have replaced Observation, controlling it, and asthem: while the seas in which they suring us that we have correctly obflourished have become lands where- served. Much has been done, and is on man in his columned cathedrals daily done, in this way, yet still men and inazy palaces emulates the beauty too easily content themselves with and syminetry of their fluted stems observation, or, what is equally faland chambered cells."*

lacious, with anatomical deduction, The delight of getting new animals declaring an organ to bave such or is like the delight of childhood in any such a function, merely because it novelty, an inpulse that inoves the resembles an organ known to have soul through the intricate paths of the function it when in most of these knowledge,-knowledge, which is

cases, direct experiment would show but broken wonder; and this delight the error of the conclusion. In forthe naturalist has constantly await- mer papers I have illustrated this ing him. Satiety is not possible, for point, and have again to do so aproNature is inexhaustible. Knowledge pos of the digestive power of the Sea unfolds vista after vista, for ever Anemones. stretching illimitably distant, the In my note-book is pencilled this horizon moving as we move. New brief query, “Do the Actinia digest facts connect themselves with new at all ?" a doubt which, in its naked forms; the most casual observation simplicity, might rouse contempt in often becomes a spark of inextin- the mind of any zoologist accidentally guishable thought running along reading it. What! here is an animal trains of inflammable suggestion. To notoriously carnivorous, and you ask this intent the naturalist should whether it can digest? Have not alwaps have pencil and note-book on you yourself repeatedly fed these his working-table in which to record animals with limpets and cooked every new fact, no matter how trifling beef? are they not greedy of such it may seem at the moment; the food? It is perfectly true. Nevertime will come when that and other theless a doubt occurred to me whefacts will be the keys to unlock many ther they did really digest, in any a casket. Not that Observation alone proper sense of the term; and I made is, as many imagine, the potent in- a note of the doubt, as of a point to strument of Zoology. Lists of details be investigated immediately on my crowd books and journals, yet these arrival at the coast. Experiment are in themselves no better than the should settle the doubt. Before narobservations of Chaldean shepherds, rating the experiments, it will be

* History of British Star-fishes, p. 2.

+ On this point, see the luminous Leçons de Physiologie Expérimentale of Claude Bernard, vol. ii.

needful to settle with the reader a polype is carried further : no sooner few generalities on the subject of does one of the filaments seize a digestion ; since, in point of fact, the prey than it retracts; all the others interest of the question falls mainly round it bend their points over the on the general subject, and only with captive, and gradually enclose it ; a secondary importance on the diges- they then retract, and bring the food tive powers of the Anemones. in contact with the body of the ani.

What are we to understand by mal. The point of contact is next Digestion ? At first the question seen to yield inwards, retracting as seems so easy; get the closer it is the filaments had retracted, and, as investigated, the remoter seems the it deepens, the food sinks into the possibility of answering it. Let us substance of the body, the edges of make a clearance by first discrimin- the cavity closing over it. In the ating Digestion—as a special function centre of the body the soluble parts of the intestinal canal—from Assimi- are dissolved, the body having relation, which is the general property sumed its original appearance. This possessed by all living tissues. For done, the insoluble parts make their an animal to grow, and to repair the way out, much as they made their waste which the action of life inces. way in ; and thus the whole process santly produces, it must assimilate, of ingestion and egestion is accomwhich, as the word implies, means plished. to separate from the external medium We need not pause to trace the such substances as are like to its episodes of the complex story of diown substance, or can be converted gestion in the higher animals, epiinto them by the vital chemistry, sodes of mastication, insalivation, rejecting all such as are unlike, or chymification, chemical transformapot convertible. Very simple or- tions aiding mechanical actions ; ganisms find assimilable food in the every one is familiar with the general element they live in, and the process facts. Let us only note that even of separation is easy : they have no milk, wbich contains all the substomach, not even & mouth, much stances needed for the nourishment less glands secreting solvent fluids. of the child, contains them in a conVery complex organisms, on the con- dition perfectly useless, as far as the trary, do not, in the air they breathe, direct and immediate nourishment of or on the earth they tread, find the the child is concerned ; until the milk variety of substances necessary to has undergone the digestive process, build up their bodies; the sub- namely, a succession of chemical destances have to be sought, captured, compositions and recompositions, it and when found, are not found in is no more competent to nourish the an assimilable condition, but in & muscles, bones, and nerves of the condition requiring great changes, child, than so much chalk and water, mechanical and chemical, before the which is delusively sold as milk in. substances are able to enter into the virtuous cities. The mutton chop, construction of the tissues.

too, which we justly reckon such exAn example will make this plain: cellent food, is only “ food potential;"* Let us first consider the process in it must undergo a very curious series the Actinophrys, a microscopic ani- of changes before it can be converted mal carefully studied by Kölliker.* into blood. Nor is the business It is a mere mass of jelly-like sub- finished there. We are erroneously stance, very contractile, without the accustomed to consider blood as the slightest trace of organs, without final stage of food, previous to its even a distinct envelope separable assimilation. · Physiologists trace the from the mass. The outer layer is story of digestion up to this point, formed into long tentacular fila- and there leave it; as story-writers ments, which, like the tentacles leave their heroes married, thereby of a polype, seize hold of young indicating that nothing more remains animalcules, or even minute crus- to be said. Bat just as marriage is taceans. The resemblance to the the beginning of a new act in the

* Siebold ů. Kölliker's Zeitschrift für Wissenschaftliche Zoologie, i. 198. VOL. LXXXI.

44

drama, and the act in which all life more fluid is secreted from the blood culminates, so is this blood-formation and poured into this canal during & but the commencement of & new single day than would make up the series of changes, and these the most whole mass of fluid circulating in important. I think it can be shown the blood - vessels at any given that the blood itself is not more im- period.t mediately and directly assimilable The reader's attention has been than the mutton chop from which it so fully directed to this twofold was formed. In its passage through agency of Digestion, and especially the walls of its vessels, it undergoes to its chemical agency, that a clear specific changes, fitting it for assimi- view may be taken of the question lation ; without such changes it is which must arise as to what, in the not assimilable ; blood, as blood, abstract, is the purpose of Digestion nourishes no tissue, but lies on it like In the abstract we may declare it to any other foreign substance which be the preparation of the food, redmust be got rid of by reabsorption in- dering it fitted for Assimilation. Bat to the veins—as we see when a vessel if we descend from heights of abis ruptured, and the blood gets depos- straction, and approach concrete ited in the parenchyma. Blood is, in questions, we soon find this answer fact, as Bergmann and Leuckart well including several processes —such as express it, a depôt of assimilable the prehension and mastication of and secretory substances; and its food, its absorption and circulation, parpose in the economy is that of a its aeration in the blood, and finally, regulating apparatus, which is ne- its transudation through the walls cessitated by the fluctuations in the of the capillaries-none of which can, procuring of food.*

without great impropriety, be called Remember, also, that before Assimi- digestive. We must be more specific lation can take place, the food must No man would confound mastication be rendered soluble. Solubility is a with digestion, or circulation with primary condition, but not the only digestion ; and we must therefore one. Many soluble sabstances have limit the term digestion to some to undergo chemical changes, both specific meaning ; mastication is the of decomposition and allotropism, be- special function of the jaws, circula. fore they form parts of the living tion of the vessels, respiration of the body. If albumen or sugar be injected lungs, and digestion of the alimerinto the veins, they will not be assi- tary canal. But even this is too milated, but cast out unaltered in the vague for our purpose; we must excretions; whereas, if injected into affix a still more specific character to the alimentary canal, or into the por- Digestion; and this may be express tal vein, which would carry them ed in the following formula : That, through the laboratory of the liver, and that only, is a specifically diges they are entirely assimilated.

tive act which takes place in an aliThus we see that solubility and mentary canal, by means of secretions transformation are the two digestive capable of chemically modifying the effects, to produce which, two agen- food, so as to prepare it for Assimilacies are needful, the mechanical and tion. chemical. From these two points The preparation of food we have all other questions expansively radi- seen to be both mechanical and ate, to them they all converge. A chemical, bat I select the latter as single fact strikingly impresses the the specific characteristic of the dimind with a sense of the extent gestive process, in order to prevent to which chemical agency reaches, confusion. Claude Bernard says: “We namely, that in the course of four- can conceive an animal without any and-twenty hours a sixth part of the digestive apparatus, mechanical or whole weight of the body is poured chemical, because living in an eleinto the alimentary canal, under the ment which furnishes nutritive me form of various secretions. Much terial directly; we can also conceive

* Vergleichende, Anatomie und Physiologie, p. 164.
+ Lehmann: Lehrbuch der Physiol. Chemie. üi. 226, 2d edit.

the digestive act reduced to a simple plex city, pot possible in a group of mechanical apparatus which has to cottages. In the same way we should press out certain alimentary juices not expect to find digestion, respiracapable of nourishing the tissues tion, sensation, or any other complex without undergoing chemical modifi- result, in animals so simple as a Sea cations; but usually the digestive Anemone. Nor could the notion act is composed of two orders of phe- ever have gained currency, had there nomena, physical and chemical."* been the proper precision in our This is a brief and luminous classifi- zoological language, and had not the cation as regards the whole animal“ fallacy of observation" misled us. series, and it well expresses the

Now to the experiments. The ascending complexity of that series ; first point to be settled was this : but inasmuch as special functions Have the polypes anything of the only make their appearance at cer- nature of a solvent fluid secreted by tain stages of that ascending series, their stomachs ? “It is obvious," inasmuch as the simpler animals have says Dr. Carpenter, the latest writer not the special functions of more on this subject, " that a powerfully complex animals, we must deny solvent fluid is secreted from the anto the two first classes of M. Ber- walls of the gastric cavity ; for the nard's series, any such special func- soft parts of the food which is tion as Digestion, and confine it to drawn into it are gradually dissolved, the third class. We do not, except and this without the assistance of in loose latitude of phrase, speak of any mechanical trituration.” Obvithe legs of an animalcule, meaning its ous, indeed, the fact seems, antil it organs of progression ; because a leg is interrogated a little more closely, is a specific organ of progression, and then we find, 1st, that no solvent apform in its elements throughout fluid is secreted; 2d, that the food the series of animals possessing is not dissolved; but only the juices legs; nor should we, otherwise than pressed out. My first experiment in easy speech, talk of the digestion was to test the presence or absence of a polype, meaning thereby its nu- of a secretion, which was accomplishtrition. The purpose of a leg, pro- ed thus : Tying a narrow strip of gression, is falfilled by the cilia litmus-paper round a small piece of which move the animalcule; the recently caught fish, and fastening it purpose of digestion, preparation of to a thread, I gave it to an Anthea food, is performed by the cavity of cereus who greedily swallowed it ; the polype ; but the specific organs, another thin slice of the same fish named legs and alimentary canal, was folded longitudinally over and the specific functions of those or- similar bit of litmus-paper, and given gans, walking and digestion, are in both to a Crassicornis. If any acid secrecases absent.

tion were present, the paper would If the reader has followed me thus redden; if not, the blue colour would far, he will bave understood that, remain. On the following morning when I doubted whether the Actinia the ejected morsels were examined, digested, there was no doubt enter- but not a trace of acid reaction was tained of their power of preparing visible. Repeating the experiment food, but only of their power of several times ander varying condichemically digesting it. I doubted, tions, I came to the conclusion that in short, whether they should not be no acid fluid was present in the diseparated from the more complex gestive process of the Actinia. There animals which digest, and whether still remained a doubt. Solvent secrethey should not rank in M. Bernard's tions are either acid or alkaline. It second class. We do not call a but was necessary to make similar exor group of cottages a city. We do periments with an alkaline reagent. not speak of its commerce, its gov. This was done, and with similar ernment, its literature; these are results. It is worth noting that M. social functions, developed in a com- Hollard equally failed in detecting

[ocr errors]

* Leçons de Physiol. Expérimentale, ii. 490.

« PoprzedniaDalej »