HYDEOZOA SIPHONOPIIORA. 



247 



they are, however, without nianubrium, 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 are 

 developed as buds formed 

 of ectoderm, entoderm, 

 and containing a central 

 cavity which communi- 

 cates with the central 

 space of the stem. In 

 the nectocalyces and 

 gonophores an ecto- 

 dermal ingrowth gives 

 rise to the covering of 

 the sub-umbrella and to 

 the generative product.* 

 respectively (fig. 1ST). 



The ova, of which 

 there is often only one 

 in each female gono- 

 phore, are large, and 

 have no vitelline mem- 



after 



im- 



undergo 



a 



regular 



brane, and, 

 pregnation, 

 complete and 

 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 hydrophy Ilium as 

 well as a pneumato- 

 phore, and the under part 

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

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



FIG. 190. Phi/sopJiora hyilruxfatica. Pn, Pneumatophore ; 

 5, nectocalyces arranged in double rows on the swim- 

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

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

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



