1 68 



PHYLUM CCELENTERA. 



the stomodaeum (ventrally). The mesenteries bear retractor 

 muscles, all situated on the sulcar aspect (see Fig. 81), and 

 each mesentery bears a mesenterial filament. The two dorsal 

 (asulcar) mesenteries are long, ciliated, and non-glandular ; 

 they are respiratory in function and cause an upward 

 current, that in the sulcus being downward. Many Al- 

 cyonarians are dimorphic, having in addition to the typical 

 polyps (autozooids) dwarf siphonozooids^ with suppressed 



FIG. 85. Corallium rubrum^ a corner of a colony. 

 After Lacaze-Duthiers. 



A., Anthocodia or retractile portion of a polyp; r.p., com- 

 pletely retracted polyp, with the verruca or calyx portion 

 left protruding; C., coenenchyma ; T., pinnate tentacles. 



tentacles, strongly developed sulcus, no rnesenteric fila- 

 ments, and often ill-developed mesenteries. Their function 

 IsT to drive currents of water through the canal systems of 

 the colony, and they are sometimes reproductive as well. 

 With the exception of one small family of solitary forms 

 (Haimeidae), the Alcyonarians form colonies which are in 

 various ways supported by spicules, or by spicules and an 

 axis. The spicules, which take the most diverse forms, 

 seem to be begun at least by ectodermic cells (a pair to 



