2S0 



ClELHELMIXTIIES 



stronglv bent alimentary canal extends into the cci?lom and is bound 

 at its liinder end bv a cord, the fiiiiiculus. to the base of the cystid. Gang- 

 lion and nephridia lie between the mouth and anus. The gonads arise 

 from the epithelium of the cojlom, the testes usually on the funiculus, 

 the ovaries on the wall of the cystid. 



Hundreds and thousands of individuals form colonies (fig. 275) in 

 wliich cvstid abuts against cystid. The ccelom of adjacent cystids may 

 be distinct or a wide communication mav e.xist. The colonies grow by 

 budding; in the Gymnobcmata a part of a cystid becomes cut off as a 



Fig. 



-Small colonv of L'jpIiol>HS cryslalliinis vafter Kraepelin), with young and old, 

 some extended, others more or less retracted. 0, statoblasts. 



daughter cystid in wldch the poh-pid — alimentary tract and tentacles — 

 arises by new formation; or (Phylactokvmata) the bud anlage of the 

 polypid arises before tlie first appearance of the cystid. 



Dinsion of labor or polymorpliism is common. Besides the animals 

 already described, which are primarily for nottrishment, three other indi- 

 Ti'iduals may occur, ovicells, vibracularia, and avicularia. All three are 

 cystids wlaich have lost tlte poh-pid The ovicclls are round capsules wliich 

 ser\-e as receptacles for the fertilized eggs. The vibracularia (fig. 274, i^) 

 are long tactile threads; the avicularia (fig. 274, A) are grasping structures 

 wliich seize small animals and hold them until decav sets in; the fragments 

 serve as footl for the poly])ids. The avicularia have the form of a bird's 

 head, the movable lower jaw being a modified operculum. 



Under unfavorable conditions a polvpid in a cvstid mav break down and be 

 lacking for some time until betlor relations cause its new formation. Besides, 

 in the depopulated cystids, there mav appear slaloblasis, internal buds en- 

 veloped in a firm envelope which form a resting stage (fig. :^75^. Each stato- 

 blast is surrounded liv a tjirdle of chambers which bv drvini; become filled with 



