niDROZOA SIPHOXOPHOU.V. 



247 



they are, however, without manubrium, mouth, tentacles, and sense 

 organs. 



The deeply concave sub-umbrella surface of the nectocalyx is 

 largely developed and has a very powerful muscular covering in rela- 

 tion to its exclusively 

 locomotive function. 

 All the appendages ara 

 developed as buds fornif-J 



of ectoderm and endo- 

 d?rm, and containing a 

 central cavity which 

 communicates with the 

 central space of the stem. 

 In the iiectocalyces anl 

 gonophores an ecto- 

 dermal ingrowth gives 

 rise to the covering of 

 the sub-umbrella and to 

 the generative products 

 respectively v (fig. 187). 



The ova, of which 

 there is often, only one 

 in each female gono- 

 phore, are large, and 

 have no vitelline mem- 

 brane, and, after im- 

 pregnation, undergo a 

 complete and regular 

 segmentation. 



A nectocalyx (Diphyes) 

 is the first structure 

 formed in the free-swim- 

 ming larva, or the upper 

 part of the body of the 

 larva gives rise to a cap- 

 shaped protective cover 

 or hydrophyllium as 

 well as a pneumato- 

 phore, and the unde?' part 

 becomes the primary nutritive polyp (Ayalmopsis, fig. 188). Since 

 new buds give rise to leaf-shaped hydrophyllia, a small stock with 



FIG. 190. Physoplwra JiydroK/uficrr. Pn, Pnemnatophcre ; 

 S, nectocalyces arranged in double rows on the swim- 

 ming column ; T, dactylozoid ; P, polyp (nutritive 

 individual) with tentacles, Sf; Nk, groups of nemato- 

 cysts on the latter ; G, clusters of generative buds. 



