SCOLEX OF A CESTODE. 79 



differentiation in D, fimbriata. Finally, in transverse sections 

 through the bothrial canal up to its point of opening on to the 

 side of the strobila, the same restriction of the bothrium to the 

 cortical layer is to be seen very plainly ; this is due to the fact 

 that here the medulla is marked off from the cortex by a thick 

 layer of longitudinal muscles which is itself sharply marked off 

 both internally and externally. The tube of the bothrium 

 traverses the cortical layer (text-fig. 4, d), only pushing back but 

 not in any way taking up or invading these longitudinal muscles. 



Text-figure 4. 



V 



Transverse section through posterior extremity of scolex of Duthiersia expansa. 



d and v, dorsal and ventral bothria forming a narrow canal in the cortical layer; 

 the external orifice of v is shown ; m, longitudinal muscular layer dividing 

 the cortex from the medulla; n, nerve-cord. 



Another difference between the scoliees of the two species 

 affects the water- vascular system. In both the scolex is per- 

 meated by a network of these tubes which is very obvious in 

 sections both transverse and longitudinal. I am not able to give 

 a detailed account of the course of these vessels in the scolex, but 

 it is quite clear that the number of tubes is much greater in the 

 smaller species D. fimbriata, and that they are here of a smaller 

 size than in the larger species D. expansa. We may now sum- 

 marise the characters of the two species as follows : — ■ 



Genus Duthiersia. 

 (1) D. fimbriata Diesing. 



Solenophorus fimbriatus Diesing, SB. Ak. Wien, 1854, p. 589. 

 Duthiersia elegans Perrier, Arch. Zool. Exp. 1873, p. 360. 



Scolex smaller ; bothria opening by continuous antero-lateral 



