DEVEI.OPMENT. 9:3 



The generative process in the freshwater Hydra offers some striking resemljlanccs to that 

 just described in Tubularia. Usually towards the end of autumn, hut occasionally even in spring, 

 peculiar tubercles may be seen budding from the body of various species of Hydra. They are 

 produced chiefly towards the anterior end of the body. I have especially examined them in 

 ffj/dra vulgaris. They are here of a conical form, and when mature have their apex perforated 

 by a short canal, through which the contents of the tubercle escape. These contents are then 

 seen to be active spermatozoa of the usual form, and the tubercle must be regarded as a male 

 gonophore.i Its external wall consists of a single ectodermal layer, and its cavity is traversed by 

 a process of the endoderm, which, at least in the younger stages, extends from the base to the 

 summit of the gonophore, where it remains for some time united to the ectodermal wall. Between 

 this axile process of endoderm, which plainly corresponds to a spadix, and the outer wall of 

 endoderm, the spermatogenous plasma is developed. The entire plasma has the appearance of 

 being divided into longitudinal masses, as if by septa, which pass from the outer wall to the axile 

 spadix. It increases in maturity as we examine it from the base towards the summit of the 

 gonophore, the reproductive elements being still enclosed towards the base in their generating 

 cells, while towards the summit they may be seen as free active spermatozoa, ready to escape 

 through the perforation which is now found in the summit of the gonophore for their exit. 



But, besides the spermatogenous tubercles, there also occur, usually on the same specimen, 

 others which, instead of containing spermatozoa, have their cavity occupied by a peculiar cellular 

 plasma, destined to give origin to ova. Their position on the body of the Ht/dra, in every speci- 

 men which has come under my observation, was at the proximal side of that part of the animal 

 which carries the spermatogenous tubercles. They form rounded elevations, with a broad base of 

 attachment, and are of less defined form than the others. They seem to be produced by a simple 

 separation of the ectoderm and endoderm of the Hi/dra, with the plasma interposed between the 

 two membranes. They certainly correspond to the female gonophore of other hydroids, but they 



simply constitute a portion of the general tissue of the plasma, as well as of the masses which are sub- 

 sequently detached from it in order to become developed into actiniform embryos. As stated above, 

 however, it is possible that the nucleated cells (PI. XXIII, fig. 22) which make their appearance at a 

 somewhat later period represent germinal vesicles. 



Claparede (' Beobacht. iiber Anat. u. Entwickel. wirbelloser Thiere an der Kiiste von Normandie,' 

 1863, p. 2) also takes a different view of the development of Tubularia from that given above. His 

 observations were made on certain minute organisms which he found swimming in the open sea, and 

 which are undoubtedly the actinula-stage of some species of Tubularia. He compares them to small 

 medusa;, the body of the actinula representing the umbrella, and the long tentacles the marginal 

 tentacles of the medusa, while that portion which is subsequently to become developed into the stem of 

 the Tubularia is viewed by Claparede as corresponding to the manubrium — the mouth of the future 

 Tubularia, with its circle of short tentacles, being developed on the summit of the umbrella. Claparede 

 believes that he had found an aperture in the extremity of that portion which is to become the stem, 

 and he has apparently been thus led to interpret this part as the manubrium of a medusa. I have 

 little doubt that Claparede has been here deceived by the peculiar structure described above, and which 

 might easily lead to an error of interpretation. 



1 We owe to Ehrenberg the original determination of the nature of these bodies. His account 

 of them is given in the ' ^Mittheilungen aus den Yerhandl. der Gesellsch. Naturf. Freunde in Berlin,' 

 1838, p. 14. 



