44 



MORPHOLOGY. 



spadix itself remains in a rudimcntal condition, being scarcely elevated above the base of tlie 

 gonophore, whose whole cavity becomes at an early period occupied by the ovarian mass. 



An advance over this condition is seen in the sexual bud which is borne by that form of 

 medusa described above, under the name of " blastocheme." Here we have the ultimate sexual 

 bud f[uite destitute of ectotheca, and reduced to the condition of spadix and endotheca separated 

 from one another by the intervening generative elements (fig. 10, p. .35). 



In Clava, Hydractinia, &c., we have a still further advance in complexity. The gonophore 

 has here the form of a simple closed sac, whose axis is occupied by a cylindrical or club-shaped 

 spadix, round which the generative elements are clustered (woodcut, fig. 1 .5, A). Careful examina- 

 tion, however, will show that the walls of the sac consist of two membranes, an outer or ectotheca 

 and an inner or endotheca. The mesotheca is entirely absent. 



In Garveia nutans, I have found a mesotheca to be distinctly demonstrable ; but it is closed 

 at the summit, and destitute of circular canal, while four short radiating canals may be seen in 

 its walls extending from the base of the spadix for about a third of the height of the sac (wood- 

 cut, fig. 15, £). 



Fig. 15. 



J b 



Types of Gonophores. 



A, Hi/dractinia ec/miala. B, Garveia nutans. C, Tulularia indhha. D, Si/ncori/ne eximia. 



o, ectotheca; 6, mesotheca ; c, endotheca; rf, spadix; rf', manubrium ; c, radiating gastrovascular canals ;/, circular 

 gastrovascular canal; g, marginal tentacles; h, ocelli; o, ova; p, ovarian plasma in Tubularia. 



Ill Tuhularia indivim the mesotheca presents the highest degree of development which 

 it attains in any adelocodonic gonophore, if we except the peculiar body described below under 



