1865.] Hincks on Zoophytes : the History of their Development. 409 



with some other cases, and probably careful investigation might increase 

 the number.* 



In Plate i., fig. la, we have a good illustration of one of the 

 simplest forms which the reproductive bud of the Zoophyte assumes. 

 It is a highly magnified representation of one of the bodies that 

 are shown in situ in Figure 1 (x — x), and it is at once apparent that 

 it exhibits a very slight advance upon the simple egg-pouch of the 

 Hydra. It is a narrow sac, formed by an outgrowth of the body-wall. 

 The central cavity (a) is in free communication with the stomach 

 of the polypite, and is visited by the common nutrient stream. It is 

 enclosed by the inner of the two membranes (6), that we have 

 described as the basis of all Hydroid structure, from which the outer 

 (c) is separated by a mass of ova. Essentially this is the sexual bud 

 of the Hydra over again. The latter, indeed, is of small dimensions, 

 and contains but a single ovum, which, as it enlarges, soon presses 

 down the inner membrane, and obliterates the central cavity, but the 

 component elements are the same in both. The differences between 

 them are of very slight significance. They amount to nothing more 

 than this, that in the present case, the external membrane is divided 

 into two layers, the outermost of which serves as a protective capsule 

 (d — d), and the bud is elevated on a kind of pedicle. To convert 

 this Gono-zooid into a polypite, little change would be needed. 

 With an orifice at the upper extremity, and a few tubular prolonga- 

 tions of the sac around it, or scattered over the surface, and minus its 

 capsular investment, it would be a very respectable Hydra. Before 

 the differentiation of the ova, it is all but identical with a polypite- 

 bud in its early stage. 



In the Campanularian capsule (Plate ii. fig. 9), the sexual zooids 

 (d — d) are of a still simpler character, and make a yet nearer 

 approach to those of the Hydra. Each of them contains only a single 

 ovum (e), which, as it increases in size, occupies nearly the whole of 

 the sac, the inner wall (e) being pressed down towards the bottom of 

 it, and forming " a shallow, saucer-shaped basis for the egg." In the 

 male zooid, however, the central cavity is large, and projects far into the 

 enveloping mass of spermatozoa. The sexual bud of the Hydra is in 

 all these points identical with that of the Campanularian^ before us, 

 which Agassiz describes as "nothing more than a double-walled 

 hernia ; " and yet, from the capsules of a Zoophyte nearly allied to 

 this, of much the same structure and general aspect, we may witness 

 the escape of those Medusa-like organisms to which so much interest 

 has attached. So that within the limits of a single family, and in its 

 most nearly allied species, we find the most widely-separated forms, 

 the simplest and the most complex, of the reproductive zooid. 



* We have met with male and female capsules together, on Halicornaria 

 (Plumularia) Calherina, on which they are thoroughly intermingled; Sertularia 

 lamarisca and S. fallaz, and r we helieve) on a species of Halecium. The Hydra 

 presents us with hoth conditions, being sometimes monoecious, and sometimes 

 dicecious, representing its Order in this, as in so many other points. 



+ Vide a paper by HaDcock, " On a species of Hydra found in the Northumber- 

 land Lakes." Ann. Nat. Hist., vol. v., 1850. 



