REPRODUCTION. If 7 



out, unless some special provision were made for its preser- 

 vation. Besides the nutritive zooids, however, other buds 

 are produced, w^iich arc morphologically identical with the 

 former, but which are greatly modified for the purpose of 

 producing the essential elements of reproduction (fig. 29, b). 

 These "generative zooids" derive their nourishment from 

 the materials collected by the nutritive zooids, since they 

 are incapable of obtaining food for themselves. Ultimately, 

 the elements of reproduction are developed, and the fer- 

 tilised ova give rise to ciliated embryos, similar to the one 

 with which the cycle began. 



In this case, therefore, the " individual " Hydradinia 

 consists of a series of nutritive zooids, collectively called 

 the " trophosome," and another series of reproductive 

 zooids, collectively called the " gonosome," the two groups 

 diifering from one another in form, but remaining in organic 

 connection. 



In other Hydroid Zoophytes nearly allied to Hydradinia, 

 the process advances a step further, and we arrive at pheno- 

 mena which we cannot parallel with anything we obser\'e in 

 plants. Up to a certain point, however, the phenomena 

 agree with those just described in Hydradinia. Thus, in 

 Clytia {Cainpanularia) we have a rooted colony or " troj^ho- 

 some " composed of a number of nutritive zooids produced 

 by continuous gemmation, and remaining organically con- 

 nected (fig. 30). The members of this colony have no 

 power of maturing the elements of reproduction ; but the 

 organism at certain seasons produces large oval horny 

 sacs (fig. 30, ^), in which generative zooids are developed. 

 These generative zooids, however, do not produce the 

 generative elements so long as they remain attached to 

 the parent colony ; but they require a preliminary i)criod 

 of independent existence. For this i)urj)ose they are spe- 

 cially organised, and when sufliciently matured they are 

 liberated from their containing capsules, and are detached 

 from the stationary colony. The liberated generative 



