DEVELOPMENT. 



103 



These formiiLx present three types of hetcromorphism. In II the heteromorphism is 

 binary (woodcut, fig. 40), in III ternary (woodcut, fig. 41), in IV quaternary (woodcut, 



fig. 4:2). 



But the hydranth mny and does in ahnost every instance — either directly or through 

 the medium of the common basis or hydrophyton — repeat itself indefinitely by budding before the 



Fig. 41. 



Fig. 42. 



Diagr.im of Corymorpha. 



A. Au entire colony, consisting of two 

 forms of zooids. a a a, the trophosorae, 

 consisting of a single hydrantbal zooid; 

 6, the gonosome, composed of many medu- 

 siform zooids. 



B. A single zooid of the gonosome after 

 having become free and attained to sexual 

 maturity. 



Diagram of Dicoryne, Colony 

 composed of three forms of 

 zooids. 

 aaa a. Tlie trophosome, com- 



posedof numerous hydranthal zooids; 



h c, the gonosome, composed of two 



forms of zooids, namely, b, bias- 



tostyle, and, c, gonophores. 



Diagram of Campanularia. Colony com- 

 posed of four ibrms of zooids. 



A. Portion of a colony, with tropho- 

 some and gonosome, a a. Trophosome, 

 showing one of the hydranths of which 

 it is composed ; 4 c, gonosome, composed 

 of three forms of zooids, namely, blasto- 

 styles, blastochemes, and gonophores; 

 b, blastostyle ; c, c, blastochemes. 



B. A blastocheme, which has become 

 free and attained to maturity, showing 

 the gonophores springing witliin it from 

 the radiating canals. 



time arrives when an element of the gonosome is to be budded off; and a series of homomorphic 

 zooids may thus introduce themselves (woodcut, fig. 41) into the heteromorphic succession, as 

 expressed in the following formula ; 



V. A+A+A+ 



&,c.-{-bls-\-gphXh-\-h-{-h-\- 



ii,c.-\-bls+gphX 



&c. 



where the hydranth becomes indefinitely repeated in the formula of ternary heteromorphism (III) 

 given above, and the same will apply to each of the other two types of heteromorphism. 



Now, in all these cases the succession from the primordial nutritive zooid to the ultimate 

 generative zooid or gonophore admits of being expressed in a continuous line ; but one or more 



