1865. j Hincks on Zoophytes : the History of their Development. 413 



process. The figure represents a portion of a shoot, on which both 

 polypite-cells and reproductive capsules are present. In one of the 

 former (a) the Hydra is seen retracted within its transparent dwell- 

 ing, b and d are two of the Gono-thecce — the horny receptacles within 

 which the sexual buds are developed, as in Fig. 9. At d one of 

 them is represented within the capsule, attached to the axial column, 

 which we have before described, as an imperfectly developed polypite. 

 While in this position it exhibits the central reproductive sac (the 

 essential element), surrounded by two investments, the inner represent- 

 ing the swimming-bell, with canals and an orifice, and a number of 

 tentacles, but no contractility, the outer being the usual protective case. 

 The generative elements are produced between the walls of the sac — but 

 the ova, at least, soon rupture the outer one, and complete their course 

 of development within the more spacious area of the swimming-bell. 

 But there is this peculiarity in the history of the sexual buds of this 

 species, — at a certain stage they are pushed out beyond the mouth of 

 the capsule, where they hang like fruit (Plate ii. fig. 8, c, c, c), until 

 the seed has ripened and escaped, when they wither away. 



(4.) In yet another case, Prof. Allman has detected in a sexual bud 

 like that of Clava (Plate i. fig. la) in most respects, the membrane 

 which represents the swimming-bell interposed between d& c, but form- 

 ing merely a closed sac — one more envelope around the ovary — while at 

 its base (a clue to its real significance) are the rudiments, the begin- 

 nings of four tubular canals. From this point a single step carries 

 us to the simplest form of bud — the polypite body, slightly modified, 

 which bears in its walls the sperm or the ova. 



We must not omit to mention that the free Gono zooid, though 

 parting from the parent stock and renouncing its stationary life, re- 

 tains the vegetative tendencies of its tribe, and, in many cases at least, 

 multiplies itself by budding. Its buds, indeed, are cast off like those 

 of the Hydra, as becomes a free being, but it preserves the customs of 

 its race. 



Our sketch of the reproductive history of the Hydroida would be 

 incomplete, if we did not add some further illustration of the struc- 

 tural identity of the nutritive Zooid — the Polypite, and the Gono-zooid. 

 Different as they are in external aspect, they are fundamentally the 

 same. This has been partially apparent in the course of our review 

 of the various grades of the sexual bud. We have easily recognized 

 in the generative sac the equivalent of the body of the polypite. But 

 we owe it to Prof. Allman's keen insight into homological rela- 

 tions, that we can also identify the radiating canals, with the tentacles 

 of the polypite, and so complete our interpretation of the reproductive 

 zooid. He reminds us that the tentacles are tubular prolongations of 

 the central cavity of the Hydra, just as the canals are of the peduncle 

 of the Gono-zooid, and that we have only to suppose them to be united 

 for a portion of their length by a membrane,* the remaining portion 

 hanging free beyond its margin, to have a structure essentially iden- 



* The tentacles of the Polypite are actually thus united in one or two species 

 of Hydroid. 



