7 W. M. WHEELER. 



It is evident that M. astcrice and M. fishcri are in many respects 

 much more closely related to each other than to any other de- 

 scribed species of the genus. Both species agree in the 

 flattened, transversely elliptical form, complete absence of cirri, 

 diffuse ramification of the male reproductive organs, position of 

 the ovary and cloacal orifice, structure of nephridia, etc. On the 

 other hand, they differ in the following important characters : (i) 

 M. fisheri is white, whereas Asteriic is buff-colored ; (2) the para- 

 podia of the former species do not project above the surface of 

 the body and are very much smaller than they are in the latter ; 

 (3) the lateral organs, too, are very much smaller in fisheri than 

 in astcrice and there is no ninth unpaired organ in the former 

 species; (4) the pharynx of fishcri is much longer, the mouth 

 nearer the anterior edge of the body ; the gut diverticula are 

 more robust and less .branched at their tips ; (5) in asteria the 

 testes and their ducts are very differently arranged. They are 

 not largely confined to the posterior half of the body, the ducts 

 are much more robust than the terminal follicles (to judge from 

 v. Stummer-Traunfels' Fig. 10, PI. 34) and there are not two 

 main vasa defer entia ; (6) the ovary of asterite is paired, that of 

 fishcri unpaired ; (7) the Mediterranean species lives in the ali- 

 mentary tract, the California!! species in the body cavity of the 

 starfish. In this respect Jishcri is quite unique among the known 

 myzostomes. The other species of the group are either free 

 ectoparasites on crinoids, like M. cirrifcrnm, or inhabit the 

 pharynx of their host (M. pulvinar) or its gut diverticula (M. 

 asterice) or live in cysts or galls which they produce in its body 

 wall or skeleton (M. cysticolitui et al). In his letters Mr. Fisher 

 is quite explicit in regard to the position of M. fishcri in the 

 ccelomic cavity of its host, so that there can be little doubt 

 about the fact. 



AMERICAN MUSEUM OF NATURAL HISTORY, 

 Oct. 27, 1904. 



