IX 



PHYLUM ECHINODERMATA 



379 





evidence that the sexual cells originate in the aboral end of the 



axial organ, and travel through the genital rachis and its branches 



to the gonads, which are to 



be looked upon as the 



greatly expanded extremi- 

 ties of the latter. Strands 



of the lacunar tissue accom- 

 pany the genital rachis and 



its branches to the gonads. 

 Reproductive System. 



The Starfish is unisexual, 



each individual possessing 



either ovaries (Figs. 313, 



314, and 315, ov) or testes, 



which appear very similar 



until they are examined 



microscopically. They con- 

 sist of masses of rounded 



follicles, like bunches of 



minute grapes a pair in 



each inter-radial interval. 



Ova and sperms are alike 



developed from cells of 



the same character as those 



which become the amoebocytes of the ccelomic and other -cavities 



of the body. The ducts, by 

 means of which the ova or 

 sperms reach the exterior, 

 open on the aboral surface 

 through a number of per- 

 forations on a pair of sieve- 

 like plates, situated inter- 

 radially close to the bases of 

 the arms. 



Anthenea flavescens (Figs. 

 313, 315, 316, 317), a 

 common Australian Starfish, 

 which may be taken as an 

 example instead of Asterias 

 rubens, differs from the latter 

 in the following main points. 



The animal consists of a 

 relatively/ large central disc 

 and five' relatively short arms, 



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showing ambulacra^ grooves ^ with ^small which taper rapidly towards 



their extremities. On the 



Fiu. 3 Hi. Anthenea, viewjof aboral surface, 

 showing granular ossicles, madreporite and 

 anus. (After Sladen.) 



FIG. 317. Anthenea, view of oral surface, 



