150 



CGELENTERA. 



SYSTEMATIC SURVEY. 

 A. Class Hydrozoa. 



There are two types, polypoid and medusoid, which may be com- 

 bined in one life history. The mouth leads directly into the gastric 

 cavity. The mesoglcea is simple, and without migrant cells. The 

 reproductive cells seem to be usually ectodermic. 



I . Order Hydromedus;e. — Simple 

 or colonial forms in which the sex- 

 ually reproductive persons are either 

 liberated as free-swimming medusoids 

 or are sessile gonophores. 



(a) Hydrophora. — Two types are 

 included here. The first includes 

 the Tubularians, Hydractinia, and 

 other forms in which the polypes are 

 not enclosed in the protective sheath 

 which often surrounds the colony 

 (gymnoblastic), and in which the free 

 medusoid forms, when present, have 

 their genital organs placed in the wall 

 of the manubrium (Anthomeduste), 

 and are furnished with ocelli placed 

 at the base of the tentacles. Hydra 

 and its allies may be included here. 



Examples : — 



Syncoryite sarsii, the free medu- 

 soid of which is called Sarsia 

 tubulosa. 



Bougainvillea ramosa liberates 

 the medusoid Margelis ramosa. 



Cordylophora lacustris and 

 Tubularia larynx have sessile 

 gonophores. 



The second type includes Campanu- 



larians, Sertularians, Plumularians, 



and others, in which the protective 



modified hydranth (blastostyle) sheath surrounding the colony is 



bearing sporosacs ; /., medusoid continued into little cups enclosing 



"person." the polypes (calyptoblastic). The 



free medusoids have their gonads 



placed in the course of the radial canals (Leptomeduspe), and are 



either "ocellate" or "vesiculate." 



Examples : — 

 Plunmlaria and Sertularia have sessile gonophores. 

 Campanularia geniculata liberates the medusoid Obelia geniailata. 

 (b) Hydrocorallinas. — Colonial forms which suggest the Hydractinice 

 in their polymorphism and division of labour, but are distinguished by 



KlG. 67. — Diagram of a gymno- 

 blastic Hydromedusa. — After 

 Allman. 



a., Stem ; £., root ; c, gut cavity ; d,, 

 endoderm (dark) ; e., ectoderm ; 

 /., horny perisarc ; p\, hydra-like 

 " person " (hydranth) ; g'., the 

 same, contracted ; h., hypostome 

 bearing mouth ; A. , sac-like repro- 

 ductive bud (sporosac) ; 



