60 SUMMARY OF CUREENT RESEARCHES RELATING TO 



supports the crystals, and so comes into contact with them. In the 

 upper wall of the terminal knob the author was able to detect an 

 ocellus. 



Sexual Cells of Hydroida.* — A. Weissmann finds that these are 

 ectodermal in origin, but he allows that in some cases they are 

 developed in the endoderm, and that in others the siJermatozoa are 

 ectodermal and the ova endodermal in origin ; and he also recognizes 

 the coenosarcal origin of the elements in some cases. Together with 

 this coenosarcal origin, there may be development from cells situated 

 in the sexual buds {hlastoid origin), and Hydrozoa may therefore be 

 spoken of as coenogenous (abbreviated from cceuosarcogenous), or as 

 hlastogenous ; and the author insists on the correctness of the view 

 that in some cases the germ- cells are not developed until the medusa 

 is completely formed. 



The chief object of the present communication is to demonstrate 

 that the sexual cells which arise in the coenosarc are uormal produc- 

 tions of great significance, and that in all such cases the coenosarc and 

 not the gonophores is to be looked upon as the true seat of the cells ; 

 and, further, to show that this mode of reproduction is very common, 

 there being entire families in which the ova are so formed; while 

 there are others in which the testicular products also are so developed. 

 Of the latter, Plumularia (e. g. P. echinulata) is an examj)le, for in it 

 the cells are developed in the endoderm, principally of the trunk 

 portion, but Often also at the base of the lateral branches of the 

 coenosarc. The formation of the male aud female gonangia is 

 described in detail, and shown to be similar for both. 



Gonothjrcea loveni is the first example of the Campauularidae, and 

 here the male elements are ectodermal, and arise, not in the coenosarc, 

 but in the gonophores, from an invaginated set of ectodermal cells. 

 The ova, on the other hand, are formed from the endoderm of the 

 coenosarc and of the branches. In Eudendr'mm ramosum they are 

 both formed from the endoderm, but the male elements are of 

 blastoidal and the female of coenosarcal origin. In Cordylophora 

 lacustris, as Schulze was the first to show, the ova are coenosarcal and 

 ectodermal ; the origin of the male elements has not been accurately 

 worked out. 



We find, then, certainly that in most (cf. next note) polyps with 

 fixed gonophores the ovules do not arise in the gonophores but in the 

 coenosarc, and their appearance is the condition of the formation of a 

 gonophore, into which they migrate. There is more variation in the 

 male products, which do not appear to be so constantly coenogenous ; 

 where, however, they are so, the development of the gonophore and 

 the migration of the testes into them is essentially similar to that of 

 the ovaries. 



Spermatozoa of Hydrozoa. t — A. de Varenne has examined 

 Camjjanularia flexuosa, Gonothyrcsa loveni, and Podocoryne carnea, in 

 which are found respectively a fixed gonophore, a demi-medusa, and 



* Ann. Sci. Nat. (Zool.), xi. (1881) art. G, 33 pp. (3 pis.), 

 t Comptes Rcnilus, xciii. (1881) pp. 1032-4. 



