This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
(130). It appears to be pretty generally admitted that among the aggregated polyps nutritive materials swallowed by one individual goes to the sustenance of the general community - an opinion seemingly based upon observations made upon certain Sertularian species: but that a similar community of nutrition exists in the Alcyonidce remained, prior to the researches of Milne-Edwards, an unsolved question; neither was anything known precisely as to the relationship existing between these aggregated beings; or, even admitting, from analogy, the most intimate union, it was difficult to conceive how nutritive matters were conveyed from one polyp to another, whether by simple imbibition or in any other manner.
(131). In order to solve these questions so far as relates to the Al-cyonidium under consideration, Milne-Edwards, by means of a small glass tube having its end drawn out fine in the flame of a lamp, injected a coloured fluid into the abdominal cavity of one of the polyps, and found that the injection immediately passed into the abdominal cavities of the polyps around; consequently the nutritive substances swallowed by any individual can be distributed among the different members of these remarkable colonies, so that food taken by one may nourish the neighbouring animals.
(132). On cutting one of these polyps open under a magnifying glass, it is easy to explain how this intercommunication is effected: it then becomes apparent that some of the animals, as described above, terminate in tubular prolongations, whereof the general substance of the polypary seems to be made up; others, however, sprouting immediately from the parietes of the former, have their internal cavity continuous with that of the larger central polyp, so that a free communication is kept up between them (fig. 27, 1), the whole forming a sort of ramified tube, or an animal having one body and one central stomach, but furnished with many heads and as many mouths.
Fig. 27. Anatomy of Alcyonidium eleguns (after Milne-Edwards.) 1. One of the branches of the polypary opened to show the communication which exists between the abdominal cavity of the principal polyp and the interior of the young ones sprouting therefrom: the apertures, it will be observed, are always in the track of the longitudinal ovarian folds. 2. Lower portion of an ovarian fold detached from the walls of the abdominal cavity to show the manner in which the ovules or gemmae are developed. 3. A portion of the foot, or basilar portion of the polypary: a, membranous tubes; 6, spicula incrusting this portion of the polypary. 4. A spiculum magnified.
(133). The development of these secondary polyps is effected by a simple process of gemmation. A tubercle makes its appearance upon the surface of the primary animal, which looks at first like a little caecum appended to the integument, having no oral aperture, but communicating freely, by means of its central canal, with the abdominal cavity of its parent. When arrived at a more advanced stage of development, the tentacula make their appearance and the alimentary canal becomes distinguishable, so that the young animal soon exhibits an exact representative of the original from which it sprung.
(134). But here it is necessary to observe that this kind of vegetation does not take place indiscriminately from any portion of the tegumentary surface of the polyp. The reproductive gemmae are only formed immediately over the track of one of the eight longitudinal membranous lamellae above noticed (fig. 27, 1), so that the apertures of communication between the newly formed polyps and the original are always so placed as to interrupt the course of one of these folds.
(135). It is not, however, only by the development of buds that the reproduction of the Alcyonidium is effected. These animals likewise produce ovules or gemmules adapted to spread to a distance their sedentary race; and it is worthy of remark that the same organs from which the gemmae above described derive their origin, perform the functions of the ovaria of higher animals.
(136). It is in the longitudinal membranous folds above described that the reproductive gemmules are developed (fig. 27, 2), which, as they increase in size, become pedunculated, and ultimately fall off into the abdominal cavity, whence they easily escape through the mouth of the polyp.
(137). The intestiniform convoluted organs (fig. 26, 1, k), situated beneath the alimentary cavity, are, from what has been stated above, evidently not the ovaria, seeing that the ova are formed elsewhere; neither, from the simplicity of the structure of the reproductive apparatus, can they be regarded as male organs destined to fertilize the ova; so that, upon the whole, it seems most probable that they represent hepatic vessels.
(138). When the polyps are expanded, their mouths are frequently seen to dilate and take in the surrounding water, which, together with such alimentary substances as may be suspended in it, penetrates into the digestive canal, and through this passes into the general cavity of the abdomen, whence again it mounts up into the tentacula through the eight canals that surround the alimentary tube. It results from this arrangement, that the thin and variously folded membrane composing the bodies of these animals is bathed throughout with the water required for respiration, and that all its internal surface is placed in contact with the nutritive matters more or less elaborated in the stomach.
(139). On seeing the same animal producing sometimes buds or gemmae, and sometimes ova, Milne-Edwards was led to inquire into the cause of this difference, which he believes to be of a mechanical nature. In those parts of the polyp which are not yet imprisoned in the growing mass of the polypary, reproduction is generally effected by the development of external buds, while towards the base of the polypary, where the constituent zoophytes are intimately united together by their outer surface, and are surrounded by a sort of sheath, no external buds are formed, but the ovules make their escape into the internal cavity of their parent. Hence the distinguished zoologist whose memoir we quote is led to infer that, on the one hand, the mechanical obstacles to be encountered, and, on the other, the excitement occasioned by the contact of the surrounding element determine this difference of procedure, and that the membrane which performs the functions of an ovary produces indifferently either ova or gemmae, according as it finds less resistance or is more stimulated upon the inside or the outside of the abdominal walls.