622 A. G. BOURNE. 



held that there is a true alternation of generations among the 

 gymnoblastic and calyptoblastic hydroids must be abandoned. 

 Asexual buds and sexual generative products both arise in the 

 trophosome, the latter, however^ become collected into specialised 

 buds which may, to the obvious advantage of the species, 

 become detached and actively locomotor, and even acquire a 

 higher organisation than the fixed trophosome. 



