ON A CESTODE FEOM CESTEACTON. 401 



covered with spinules; and a similar case had previously 

 been observed by Pintner. 



The early separation of the proglottides in this and other 

 species is obviously correlated with the free locomotive habits 

 of the strobila. With a much longer train of connected 

 proglottides, the posterior loaded with eggs, such movements 

 would be rendered difficult or impossible. The spiral valve 

 in the intestine of the Elasmobranch renders it possible for 

 the separated proglottides, without definite organs of adhesion, 

 yet Avith an adaptation for creeping movement, to remain 

 within their host until such time as the uterus has become 

 fully charged with eggs. 



This Cestode is to be referred to the genus Phylloboth- 

 rium of P. J. van Beneden. In the definition given by that 

 author^ the bothridia are described as notched externally, 

 but the notch is not present in one of van Beneden's own 

 species (P. auricula), and cannot be looked upon as of 

 generic importance. I propose the name of P. vagans for 

 the Cestracion parasite, which appears to be distinct from all 

 the species described hitherto." 



The only species of Phyllobothrium, of the structui-e of 

 which a detailed account has been published, are P. thridax 

 and P. D o h r n i i. These have both been pretty fully described 

 by Zschokke (20, p. 327 et seq.); but, as mature segments 

 were not met with by that author, many features of import- 

 ance, more particularly in the reproductive apparatus, Avere 

 overlooked. 



Integument and Nervous System. 



The cuticle (fig. 4, cu.) is homogeneous and not divided into 

 layers. Immediately beneath it are the usual external longi- 

 tudinal (e. I. m.) and circular (e, c. on.) layers of muscular 

 fibres. The subcuticular cellular layer is much better 

 developed in the strobila than in the free proglottides, in 



' 1, p. 120, and 2, p. 123. 



^ I have not seen the original description of P. gracile, Wedl., from 

 Torpedo marmorata.but only the brief defiiiilion given by Lonnberg (11). 



