“In the Mediterranean there is a rich family of splendid swimming-polyps, which Carl Vogt in particular (“Recherches sur les Animaux infèrieurs de la Méditeranée”) has brought to the knowledge of the scientist. A young polyp is developed from an egg. It begins its life freely floating in the sea. At its upper end it forms a bubble, in which the air is set free which supports it; at its lower end there are formed, in ever richer and fairer measure, feelers and prehensile threads with special urticating organs. On its stem, which is continually elongating, there is formed a filtering tube. From this stem arise bud-like shoots. Some of them form swimming bells, which propel themselves, and consequently the whole mass. The others are metamorphosed into fresh polyps, which possess mouth and stomach, and not merely collect, but also digest food for the whole, to deliver it finally into the common trunk-tube. Finally, yet other buds attain a nettle-like aspect, and provide for propagation; they bring forth ova, from which again proceed freely-floating polyps.” (Special polyps with long sensitive tactile threads represent the sense-organs or the intelligence of this state.) “What is here individual? The young polyp appears to us simple, but out of it there is formed a stem like a plant. The stem sends out tentacles like roots, but they move voluntarily, and grasp prey; it forms a trunk with a digestive sac, but it has not any more than the plant a mouth to make use of the sac. It sends forth buds and sprouts like the plant, but every bud has a special task, which it performs with the appearance of original activity. Special sprouts or branches endowed with movement of their own manage, some the reception and digestion of the food, others propagation. The trunk is nothing without the limbs, the limbs nothing without the trunk” (Virchow, “Vier Reden,” pp. 65, 66). Whoever holds fast to the “either-or,” certainly such an example must reduce to desperation; but we see in the several members individuals partly of polyp-form, partly medusoid, and, in the whole, an individual of higher order, which includes in itself all these individuals. Even in the bee- and ant-hive there is nothing wanting to complete the view of the whole as an individual of higher order but spatial unity, i.e., the continuity of the form; here this likewise is present, and therefore the individual is indisputable.
This widespread phenomenon in the animal and vegetable kingdom of a varied physiological development of morphologically originally similarly constructed individuals of the same species is termed Polymorphism (even the separation of the sexes comes under this conception). Kölliker recently discovered an interesting example in the family of the sea-pens (Pennatulidœ). Without entering into the morphological significance of the organs of the trunk, which serve as supporters of the several animals, it is to be said that here the sex-animals, devouring animals, and feeling-animals are not different, but one; on the other hand, stunted individuals without tentacles and sexual organs occur, which used to be regarded merely as warts (granulation), of the skin, but which otherwise possess altogether the structure of the sex-animals, and perhaps have a particular relation to the imbibing and venting of water. It is one and the same principle of division of labour, of the facilitation of a collective performance by distribution to various one-sidedly endowed organs, which, in the organised state of the bees, and still more in that of the ants, conditions the different development of from three to five separate individuals, and that here he assigns the system of movement, of assimilation of food and digestion, of perception and propagation to diverse individuals coalescing into an individual of higher order. It is just this principle, however, which we find also carried out in the higher plants, where the roots provide for the reception of nutriment, the leaves for respiration, the flowers for propagation, whilst a trunk or stalk gives support or cohesion to the whole, as the middle stem of the floating polyp commonwealth. As in the bee-state the sexual activity is personified in drones and queen, so also in the diœcious plants, i.e., in those in which the one plant bears merely male, the other merely female flowers; and in the monœcious, where male and female flowers are on one plant, are these flowers not to be called individuals, because they happen to be united in space by other parts of the plant?
But not merely in the remote region of lower marine animals do we thus manifestly find compound individuals. The comprehension of the tape-worms, in which the head, by means of so-called nurse-generation, produces an entire colony of hermaphrodite sexual animals, leads us to the correct estimation of the anatomical structure of the annelids, and these guide us to that of the articulata. In the lower Annulata each segment has its gills, its expansion of the intestinal canal, its contractile distension of the large blood-vessel, its ganglia, its ramifications of the nervous and vascular trunks, its organs of propagation, its locomotor appendages, and sometimes even its special pair of eyes. Among the Articulata the Myriapoda stand nearest to the Annelids; the process of gemmation of segments, which is characteristic of the compound individual, is here in part to be very distinctly observed in the embryological history of development; the larva of the milliped, which is hatched with eight segments, forms, even in the first moulting, between the ultimate and penultimate segment six new ones. In the degree in which the division of labour and perfection of the type progresses from the tape-worms to the Annelids, to the millipeds and from these to the higher Articulata (crabs, spiders, insects), in the same degree is there exhibited an intensified differentiation of the segments of which the compound insect consists; but even in the most perfect insects, with the assistance of the individual and the palæontological history of development the composition from segments, which are conceived as originally independent, is still more certainly to be made out, and however far the differentiation may otherwise be carried, there yet remain certain functions (e.g., respiration) here always decentralised.
The successive segments of the Vertebrata, which consist of a vertebra with its osseous processes, together with the appertaining muscular, vascular, and nervous pairs, unquestionably exhibit a certain analogy with these successive pieces of the compound worms and millipeds. Nevertheless this does not seem to me sufficient to place, with Häckel, both forms on the same level of individuality, because in the compound worms the manifold of the collective individual arises by aggregation of many single individuals, but in the Vertebrata by internal differentiation. It makes no difference here whether the several individuals are the result of sexual congress, or whether, as in the tape-worm, they are produced from an originally simple individual by way of nurse-generation; both form a mutual contrast to the interior, gradually progressive differentiation of the vertebrate organism, whose prototype, the Amphioxus, forms by no means the analogue of a compound, but of a simple worm. The course of development in the Invertebrata and Vertebrata is accordingly an exactly opposite one. In the former it is the manifold, which concretes to unity in increasing measure by means of unlikeness and closer connection of the parts; in the latter unity is the starting-point, which unfolds to the wealth of the manifold by enhancing the inner multiplicity; in the former case the individuals of lower order grow together to an individual of higher order; in the latter case an individual unfolds into individuals of lower order, and thereby at least relatively enhances the degree of its order of individuality. Thus it becomes intelligible that, in spite of the opposite starting-point, both courses of development approach one another so much nearer in their results the farther they have progressed, i.e., the more closely on the one side the composing members have coalesced, and the more they have converted their functions, fulfilling originally merely particular aims, to serviceable functions of the higher whole,—the farther on the other side the inner differentiation of the successive portions, organs, and systems of organs has advanced.
As the above-mentioned floating polyp-stocks and l’ennatulidæ are remarkable for the several individuals composing them being entirely lowered to the rank of differentiated organs of the higher collective organism, so conversely we see that in the higher animals the organs obtain the more sharply defined individuality, the more strongly they are differentiat
ed in their functions and their constitution. One may again distinguish within the organs three essentially different grades of individuality of organ; the simple, the compound organs, and the systems of organs. The simple organs (Häckel’s organs of first and second rank) consist of a tissue of one kind; the compound of that of several kinds; the systems of organs are the indivisible union of a number of single and compound organs in the whole organism, so far as they serve a particular functional purpose. Simple organs are, e.g., the epidermis, whose appendages (hairs, nails, scales, cutaneous glands, crystalline lens), cartilage, and several other vascular and nerveless forms of the connective tissue; compound organs are such as the several muscles, nerves, bones, blood-vessels, mucous membranes. The sense-organs are mostly of so complicated a nature that they conduct us from the organs to the systems of organs, e.g., the sum of the endings of the tactile nerves beneath the epidermis. As system of organs one may further cite the protective system of the surface of the body (epidermis with appendages), the system of the skeleton, the muscular system, the nervous system, the vascular or circulatory system, the intestinal or digestive system, the respiratory system, the generative or reproductive system. Of course between these different systems in the higher animals there takes place a very intimate interpenetration and interlacing; still even morphologically their separation can very well be accomplished, and there is no apparent reason why the more intimate fusion should afford a motive for doubting the relative individuality of these systems, which is so glaring in the floating polyps in spite of the local fusion and in the communities of bees and ants is developed even to the partition of functions among discrete individuals. In the spatially more sharply defined simple or compound individual organs the acknowledgment of individuality should meet with still fewer difficulties; as certainly as to the single leaf or stamen of the plant belongs a kind of individuality, so certainly to a hair of a man’s bead does a sort of individuality appertain. In lower animals single organs sometimes testify their individuality by releasing themselves from the collective organism, and yet go on living and regularly perform the office for the sake of which they are there; thus, e.g., in several kinds of Cephalopods (Argonauta, Philonexis, Tremoctopus) the males have a hectocotylus, i.e., an arm elaborated into a sexual organ, which performs the pro-creative act by being liberated from the male and penetrating into the female. This hectocotylus was at first regarded as a parasite, afterwards as the rudimentary male of the respective cuttlefish, until it was perceived to be the individualised organ of the male.
Of importance for our theme is likewise the pathological conception of parasitic formations. I shall let an authority in this field, Professor Virchow, speak for me. (“Cellular Pathology,” pp. 427, 428): “Let one only remember that parasitism only gradually comes to mean something else than the notion of autonomy of each part of the body. Every single epithelial and muscular cell leads in relation to the rest of the body a kind of parasitic existence, just as every single cell of a tree in relation to the other cells of the same tree has a special existence belonging to it alone, and withdraws from the rest of the elements certain matters for its needs (ends). The notion of parasitism in the narrower sense of the term is developed from this conception of the independence of the several parts. As long as the need of the remaining parts presupposes the existence of any part, as long as this part is useful in some way or other to the other parts, so long one does not speak of a parasite; it becomes so, however, from the moment when it is foreign or injurious to the rest of the body. The conception of the parasite is therefore not to be confined to a single series of excrescences, but it belongs to all plastic (formative) forms, but before all to the heteroplastic, which in their further elaboration do not produce homologous products, but new formations, which are more or less unsuitable in the composition of the body (at this particular place).” From the unmistakable individual independence of the parasites and the purely gradual difference between them and normal formations one may also regressively conclude to the individual independence of the latter.
Still more distinct is the individual independence in those structures which exhibit also morphologically a certain local separation from the rest of the body, and yet in their independent functions produce an effect subserving the ends of the entire organism. I may mention, e.g., the seminal filaments. The time has gone by when the spermatozoids were regarded as independent animals analogous to the intestinal worms destitute of mouth and stomach, for the purpose of their existence and above all their developmental history testify to the contrary. Nevertheless we cannot deny to these structures an individuality. In the diluted semen the filaments may be seen to contract, to revolve on their axes, lash with their tail, jerk forwards the head, and freely float about in all directions, the wriggling or screw-like motion of the tail effecting the movement. These movements appear most arbitrary in the spermatozoids of the animal species where fertilisation is most difficult, i.e., in the mammalia, and become the more simple and regular the more easy in the ascending animal scale fertilisation becomes by the number, size of the ova, and arrangement of the place of fertilisation. That a certain dependence of existence on particular surrounding external relations, or even a linking with the existence of other organisms, does not disprove individuality, we have already mentioned before (one has only to think of parasitic animals); but the spermatozoids have also a tolerably long life outside the seminal fluid in every blood-hot, chemically indifferent fluid, if they are only not hygroscopically deformed by the same. In the female organs of generation of the mammalia they continue to live for days, nay, weeks; and in the seed-pouches, e.g., the male river-crawfish, which, in the rut, attach to the females in autumn, or in the seminal vessels of humble-bees and wasps that have copulated in the autumn, they continue to live until the spring, to then fertilise the ova which have in the meantime become ripe. This already proves a high degree of independent vital capacity after the separation of the organism producing them. The morphological type of all spermatozoids of the whole animal kingdom are the zoo spores of the Protist kingdom, structures of whose individuality hardly a doubt could well be suggested. It is just the zoo spores of the lower organisms which exhibit the extremest degree of individual independence (in the Myxomycetes the spores even increase for several generations by fission), and nevertheless many of them surrender the same in the act of copulation, in which two or more individuals lose their individuality and blend into one new individual. In the copulation of the zoo spores we have to see the prototype of the fertilising act, in which likewise two individuals (ovum and seed-filament) allow their individuality to become lost in that of a single new individual. When the plasmodes of the Mynomycetes in their apparently lawless creeping about now disintegrate, now flow together into one, we shall perceive therein a phenomenon merely of life and growth. We see, then, how near procreation stands to growth even in reference to the act of copulation of the materials of generation, if we compare with the confluence of two plasmodes the congress of a number of zoo spores to form a plasmode. If here only a summation of like individual forces appears to be intended, the thought is forcibly suggested of a neutralisation of invisible individual differences in a copulation of two zoo spores, until in sexual generation this difference rises to the height of a characteristic contrast of the generative substances.—If one should attempt to dispute the autonomous movements of the spermatozoids by a parallel with the movements of cilia, I should reply that in my view conversely the autonomy of the former makes for that of the latter. An alternating movement of a structure separate in form, which demonstrably neither follows on mere external stimulus nor is even produced by central parts, since it persists after the isolation of the smallest portion of ciliated epithelium, must arise from a cause inherent in the structure itself, i.e., bears the character of a certain individuality. That the movements of the ciliary hairs of a surface frequently agree with one another in such a way that regular total movements, continuous waves, &c., arise, cannot we
aken this opinion. The like is also found in the bundles of spermatozoids, where in each bundle regular waves flow on one after another, or in those which are deposited together in a thickly packed mass (e.g., in the earth-worm), where the beautiful, regular waving is said to be comparable with that of a cornfield. It is just the same co-operation of many individuals towards a goal as in the organism in general.
There are Protista (Amœba diffluens and porrecta) whose sole locomotion consists in this, that they shoot out rays in which the substance of the animal combined with the points flows after one, or even several, whilst the previous centre is thereby narrowed to the ray remaining behind, which now withdraws to the new centre of gravity. On precisely the same principle (according to Van Recklinghausen) pus corpuscles move as long as they are living; they too shoot out radiated processes at the periphery, and withdraw the same; and at times one observes that the viscous content of the cell darts after into such a ray. The identity of these pus corpuscles with the most common form of the white lymphatic bodies was subsequently demonstrated by Cohnheim, and their exit at the place of suppuration established. Then Virchow observed similar phenomena of movement in the large-tailed cells which are found in a just excised cartilaginous tumour. Movements had already been discovered in the blood corpuscles of several animals. Without desiring to place the pus corpuscle and similar freely moving structures morphologically, chemically, or physiologically beside the corresponding lower animals in any way, from which they are so entirely distinguished by their historical development, I yet think that they may lay claim to an equal right of individuality with those, since they, if not animals in the zoological sense, are yet beings which move about in their environment just as purposively and with the same appearance of voluntariness and animation as the lower infusoria. That the circumstances of nutrition are accommodated to the medium entirely answers to the general processes in organic nature, and that they have accordingly no mouth and stomach, cannot detract from their individuality, since there are indeed animals also in whom both are wanting.
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