Volume 4

The cyclopaedia of anatomy and physiology / edited by Robert B. Todd.

Date:
1836-1859
Catalogue details

Licence: Public Domain Mark

Credit: The cyclopaedia of anatomy and physiology / edited by Robert B. Todd. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    animal, are prolonged into a common canal, their opposite extremity tapering to a point as the eggs become smaller, each ovary con- taining about sixty eggs. The common tubes of two neighbouring ovaries unite into one as they issue from the longitudinal cavity, and this again joins the common canal of the next pair; the resulting duct, which is thus common to four ovaries, opens into the stomach. The openings of these terminal tubes are arranged in a zig-zag direction, some opening lower down, others higher up. Reaumur* beUeved that the young issued by a slit on each side of the body, situated beneath the fold of the muscular envelope that surrounds the bases of the tentacula, but the supposed openings are merely folds of the skin, never perforate, and not always present. Nevertheless, as the tentacula are perforate at their extremities, and water is frequently forced out of the body through these open- ings, it is possible that some ova may become detached and issue through these organs. The ova are round, yellow, and like little grains of sand. Ellis, Reaumur, Dicquemare, and Spix, all assert that Actiniae are vivipa- rous. The latter observer states, 1 have several times seen them issue from the mouth of their parent perfectly formed. An Actinia that I have in spirit of wine contains a great number of eggs, each marked with an opaque spot that seems to contain the young animal. I have even one individual not larger than a hemp-seed, which seems hardly ready to quit its envelope, having neither the mouth nor the tentacula perfectly distinct. Moreover, I suspect that the eggs are sometimes hatched in the ovaria or in the stomach, and some- times out of the parent. I am not sure but the animal may at the time of the expulsion of the esgs have its stomach turned inside out. The number of eggs must be prodigious, each Actinia possessing upwards of a hundred ovaria. It appears from recent researches that the Actiniform polypes are bisexual. It is rendered extremely probable by the very advanced condition of the muscular ap- paratus in the Actinia that they likewise possess a nervous system. Spix in his ex- periments employed galvanism, which made the animal contract convulsively, and finding that the contractions were strongest in the neighbourhood of the base of the animal he was led to search for it in this part, and con- ceived that he had discovered it in this situ- ation. Having raised by a slight incision the longitudinal muscles at their union in the middle of the base, I perceived with a magni- fying glass an interlacement formed by some pairs of nodules disposed around the centre which communicated by several cylindrical threads ; from each nodule two filaments ran forwards; one was seen to run aloiig the muscle, the other to pierce it, to divide into * Histoire de rAcademie des Sciences Xatiu-elle?, An. 1710. two branches, and, lastly, to lose itself in the longitudinal cavity formed by the floating muscles. The situation of the nodules and filaments is beneath the stomach, and their round figure would not allow me to confound them with the muscles, which are broad and riband-shaped, and still less as the latter putrified rapidly, while the former remained entire.* Some of the tropical Actlni^ef, which oc- casionally measure a foot in diameter, pro- duce a stinging sensation when they are handled, and this stinging property is even communicated to the water that they absorb. There is moreover one remarkable circum- stance connected with it; namely, that it acts much more powerfully upon the skin, which it inflames, than upon the mucous membranes, and a drop received into the eye causes much less pain than when applied to the eyelids. The Actiniae, although exceedingly vora- cious, will bear long fasting : they may be pre- served alive a whole year, or perhaps longer, in a vessel of sea-water; but when food is pre- sented one of them will devour two mussels in their shells or a crab as large as a hen's egg. In a day or two the shell is voided at the mouth perfectly cleared of the meat. Their power of reproducing lost parts is scarcely inferior to that of the Hydras. The Abbe Dicquemare | describes some experi- ments on this subject, and states that when a horizontal section is made through one of these creatures the tentacles still seized and swallowed food, which sometimes passed through the body, at other times was expelled from the mouth digested. In about two months tentacles grew from the other portion, and it ate food, soon becoming a perfect ani- mal. He states that in this way he even succeeded in making an Actinia with a mouth and tentacles at both ends ! AuLOZOA. — The third subdivision of Po- lypi fer a is composed of a series of zoo- phytes very different in their organisation from those embraced by the two preceding. They have generally been named by natu- ralists Tubular or Vaginated Polypes, and are distinguishable from the circumstance that their living substance, instead of being external to the hard pol\pary, is in them enclosed in a calcareous or corneous tube, sometimes simple, but more frequently rami- fied, from which the polypes are protruded, either through a tei'minal aperture or from lateral cellules formed by the external en- velope. The Aidozoa are divisible into several groups, which we shall separately examine, beginning with the Tiibu/aridce. In the Tubularia {Jig. 48), as in all polypes unproviiled with a complete digestive canal, there is an organic portion which brings all the members of the colony into communica- * Spix, Aim. du ]\Iiis. d'Hist. Xat. vol. xii!. p. 444. t Qi^oy et Gaimard. X Phil. Trans, for 1773.