OF ZOOIDS IN THE HYDKOIDA. 



99 



directly applicable to particular cases of heteromorphic succession in the life of 

 the hydroid, we shall obtain the following formulae, where h is used for the 

 hydranth, Us for blastostyle, bkh for blastocheme, and gph for gonophore — 



ii. 1 1 



h + gph x h + gph x &c, Corymorpha. (fig. 1.) 



III. | >h + bis + gph x h + bis + gph x &c, Dicoryne. (fig. 2.) 



a i 



IV. I >h + bis + blch +gph x h + bis + bkh + gph x ...&c, Campanularia.(fig. 3.) 





These formulae present three types of heteromorphism. In II. the hetero- 

 morphism is binary, in III. ternary, in IV. quaternary. 



Fig. 1. — Diagram of Corymorpha. 



A, the entire colony composed of 

 trophosome and gonosome ; aaa, 

 the trophosome, consisting of a 

 solitary zooid ; b, the gonosome, 

 consisting of numerous zooids. 

 B, a single zooid (gonophore) of 

 the trophosome become free and 

 mature. 



Fig. 2. — Diagram of Dicoryne. 

 a aaa, the trophosome, consisting 

 of numerous zooids ; b c, the 

 gonosome, consisting of blasto- 

 style, b, and gonophores, c. 



Fig. 3. — Diagram of Campanularia. 

 A, portion of the entire colony ; a«. 

 the trophosome ; b c, the gonosome ; 

 b, blastostyle ; cc, blastochemes. E, 

 a blastocheme become free and 

 mature, and carrying within its bell 

 special zooids, which are the ulti- 

 mate sexual buds or gonophores. 



But the hydranth may and does in almost every instance — either directly 

 or through the medium of the common basis or hydrophyton — repeat itself 



