S YSTEMA TIC SUR VE Y HYDROMEDUS&. 



163 



forms, Protohydra leuckartii and Halennita cumulans, which may turn 

 out to be larval. 



Examples : 



Syncoryne sarsii, the free medusoid of which is called Sarsia inbulosa. 

 Bongainvillea rainosa liberates the 



medusoid Margelis rainosa. 

 Cordylophora laciistris and Tubitlaria 



larynx have sessile gonophores or 



sporosacs. 



The second type includes Campanu- 

 larians, Sertularians, Plumularians, and 

 others, in which the protective sheath 

 surrounding the colony is continued into 

 little cups (hydrothecce) enclosing the 

 polypes (calyptoblastic). The free medu- 

 soids have their gonads placed in the course 

 of the radial canals (Leptomedusie), and 

 are either "ocellate " or " vesiculate.'' 



Examples : 



Phumtlaria and Scrhtlaria 



sessile gonophores. 

 Campanularia 



have 



geniculata liberates 

 the medusoid Obelia gt-nicitlata. 



(b) Hydrocorallinae. Colonial forms 

 which suggest the Hydractinke in their 

 polymorphism and division of labour, but 

 are distinguished by their power of taking 

 up lime, and so forming "corals." The 

 colonies are complex and divergent, the 

 reproductive persons are probably sessile 

 gonophores, but a simple male medusoid 

 has been described. Millepora, Stylaster. 



(c) Trachymedusae. - - These exist only 

 in the medusoid form, and are divided 

 into two groups, Trachomedusae and 

 Narcomedusae, according to the position 

 of the gonads. 



Geryonia, Car marina, Citnina, 

 Aeginopsis. 



2. Order Siphonophora, Free-swim- 

 ming colonies of modified medusoid persons 

 (medusomes), with much division of labour. 



Physalia (Portuguese man-of-war), Diphyes, Velella, Porpita. 



Graptolites. Extinct unattached colonies with a rod-like axis found 

 in Upper Cambrian, Ordovician, and Silurian systems. The colony is 

 usually linear, and consists of cup-shaped hydrothecae borne on one, 

 two or four sides of the solid axis (virgula). Each opens into a common 



I. 



FIG. 78. Graptolites. 



I. Monograptus. 

 II. Diplograptus. 



