THE GONOSOME. 63 



itself by two different kinds of eggs. In accordance with this view, he called the female gono- 

 phores in his Sertularia {Eudciuhium) raceiiiosa "nova a racemo," and the male gonophores 

 " nova a corimbo."^ 



The differences above described between the male and female are all confined to the 

 gonosome ; the trophosome, however, does not appear to be always exempt from a participation 

 in sexual difference, for in Hydradinla polyclina, Agass., the hydranths of the male colony 

 are described by Agassiz as differing from those of the female colony by their more elongated 

 proboscis.^ 



We may now consider how the principal modifications which we have described as presented 

 by the gonosome are distributed among the leading groups of the Hydroida. 



There is no fully established instance of the same species of hjdroid producing both 

 phanerocodonic and adclocodonic gonophores, either simultaneously or consecutively ; and Sars' 

 is certainly in error when he includes under his Podocoryne carnea, two forms of hydroids, 

 one with developed medusae, and the other with sporosacs. Neither is there any known instance 

 of a species with blastochemes producing gonophores in any other way than through the medium 

 of the blastocheme, and there can be little doubt that Van Beneden* has made some confusion 

 between two distinct species when he figures a portion of a hydroid colony, which he names 

 Campanularia (/enicuJata, with two kinds of gonangia, one containing medusae and the other 

 sporosacs. 



Among the gymnoblastic hydroids the gonophores may be borne either l)y the trophosome 

 directly or by blastostyles, but they are never included within a gonangium. We have here 

 some species with phanerocodonic and others with adclocodonic gonophores, and the two forms 

 would seem to be pretty ecpially distributed through the group. Unless Nemojysis should prove an 

 exception, there is no known example of the occurrence of a blastocheme among the Gymnoblastea. 

 It is, however, by no means impossible that the sexual lobes of Nemopsis whose bases extend 

 over portions of both the manubrium and radiating canals, ought to be regarded as true zooids. 

 If this be so, then the Nemopsis medusa must be regarded as a blastocheme, though M'Crady 

 has shown that its trophosome is that of a true tubularian. 



Among the CampamdarincE we meet with medusiform planoblasts, as well as with fixed 

 sporosacs, both forms being produced in nearly equal proportion. The planolilasts, however, belong, 

 with only a single known exception, — that, namely, which is afforded l)y Leptoscijpjlms tenuis — • 

 to the type of the blastocheme. Both planoblasts and sporosacs are in the CampanalariucB 

 always developed upon blastostyles within a gonangium. 



The Geri/onidcB, a group composed of medusae which have not yet been traced to a hydraform 

 trophosome, must probably, as we shall see below, be regarded as true blastochemes. 



Finally, among the Serfularince we know as yet of no instance of a planoblast, the gene- 

 rative elements being among these hydroids always produced in fixed sporosacs, which, as in the 

 Campanidarina:, are invariably borne on the blastostyle of a gonangium. 



' Cavoliui, ' Mem. Polypi Marini,' 1785. 



^ Agassiz, ' Nat. Hist. United States/ vol. iv, p. 228. 



' Sars, ' Fauna lit. Norv.,' p. 7, pi. ii, fig. 5. 



* Van Beueden, 'Mein. sur les Canipanulaires,' pi. iii, figs. 1 — G. 



