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.
The tube is of a yellowish-brown colour, sufficiently translucent to reveal a core or central axis of flesh running along its centre and sending off branches into the polyp-branchlets, from the open lips of which the flesh emerges in the form of a thickened oblong head, somewhat club-shaped, whence the name Coryne (from Kopvvn, a club.) The tube or sheath becomes membranous, or rather gelatinous, at its margin, the ultimate three or four rings being evidently soft and scarcely consistent, of undefined outline, and larger than the rest. The club-shaped head of the polyp is studded with short tentacles, of curious and beautiful structure. These vary much in number in each polyp; but the full complement appears to be from twenty-five to thirty, arranged somewhat in a whorled manner in four or five whorls, which, however, especially the lower ones, are often irregular and scarcely distinct. The tentacles spring from the axis, with a graceful curve; they are rather thick and short when contracted, but slender when elongated, and nearly equal in diameter, except at the termination, where each is furnished with a globose head studded all over with tubercles, each of which is tipped with a minute bristle.
The neck or body of the tentacle is perfectly transparent, and appears to be a tube with thin walls, but containing a colourless thickish axis freely permeating its centre, marked with delicate parallel rings. The tentacles are endowed with the power of free motion, and they frequently throw themselves to and fro with considerable energy. The whole polyp likewise can be tossed together from side to side at pleasure.
* Rambles on the Devonshire Coast. 1853.
In the Tubular Hydrozoa the structure of the tentacula is widely different from what has been described in Tubipora musica and other anthozoic polyps. When the Tubularia is expanded, its protruded portion is seen to be furnished with two circles of arms, one placed around the opening of the mouth, the other at a considerable distance beneath it (fig. 41, l); and, nearly on a level with the inferior circle, a second aperture (fig. 41, l, a) is observable, communicating with that portion of the body which is lodged within the tube, and resembling a second mouth. A remarkable action has been observed to take place in these parts of the polyp, producing a continual variation in their form*: a fluid appears, at intervals, to be forced from the lower compartment into the space intervening between the two rows of tentacula, which becomes gradually dilated into a globular form (fig. 41, 2,3).
* Lister, "On the Structure and Functions of Tubular and Cellular Polypi," Phil. Trans. 1834.
This distension continues for about a minute, when the upper part, contracting in turn, squeezes back the fluid which fills it into the lower compartment through the opening a, which then closes preparatory to a repetition of the operation. The intervals between these actions were, in the specimen observed by Mr. Lister, very evenly eighty seconds. In Tubularia indivisa the sheath or cell, b, which encloses the polyp is perfectly diaphanous, allowing its contents to be readily investigated under the microscope. When thus examined, a continual circulation of particles is visible, moving in even, steady currents in the direction of the arrows (fig. 41,1) along slightly spiral lines represented in the drawing. The particles are of various sizes, some very minute, others apparently aggregations of smaller ones; some are globular, but they have generally no regular form.
(195). The mode of propagation in Coryne, Tubularia, and other genera of Hydriform polyps has occupied the attention of many diligent inquirers, the results of whose labours are extremely interesting and important; it is, however, to the researches of Professor Van Beneden that science is principally indebted for information upon this subject. According to the observations of that indefatigable naturalist*, the reproduction of these zoophytes is effected in no fewer than three different ways: -
1. By continuous gemmation.
2. By the production of free gemmae.
3. By simple ova.
(196). Observation has moreover shown that in every species propagation is effected by more than one of these modes of reproduction, and sometimes by three or four; and it must be remarked that in none of them is the cooperation of a male apparatus requisite, neither have any male organs or spermatozoa been as yet detected.
(197). Development by continuous gemmation is the simplest possible and is effected by mere growth from the original polyp at certain determinate points of its substance, which points are similarly situated with respect to each other in all the individuals belonging to the same species. At these points appear gemmae exactly similar, both in texture and mode of growth, to the body from which they spring; and the buds thus produced give birth to others in a precisely similar manner.
Fig. 41. Tubularia indivisa.
* Nouveaux Memoires de l'Academie de Bruxelles, 1843-1844.
(198). In like manner when a stem is cut off transversely, a bud is developed from the cut extremity, which by its growth prolongs the original trunk. When this kind of gemma has attained to a sufficient size, there arises from its extremity a little crown of tubercles j subsequently a second becomes manifest, at some distance from the first; and as the growth of these tubercles continues, each of them becomes at length developed into a tentacle. The tentacle, therefore, grows from the body exactly in the same way as the bud from the stem, the only difference being that the former is solid, and the latter tubular.
(199). The growth of the horny sheath of the polypary (fig. 42,6) exactly keeps pace with the development of the soft substance, and even advances beyond it.