86 ANIMAL PAEASITES. 



part of the body, but probably in the ring uniting the four 

 vessels, which runs round the rostellurn of those Cestodea which 

 possess a rostellurn,, or in the simple transverse uniting branch, 

 which occurs in the anterior part of the head of those Cestodea 

 which have no rostellurn. In favour of this view we have not 

 only the absence of a strong communicating branch or ring of 

 this kind in the anterior part of the body in the Trematoda, but 

 also the well-known observation, that in the microscopic examina- 

 tion of uninjured Cestodea the cephalic vessels may be very 

 easily recognised by the employrnent of only a moderate pressure ; 

 that this also succeeds very well when the colony is wrapped 

 round like the renverse of a bandage, and cut off behind this 

 part. The vessels of the head also and those of the anterior 

 part of the body immediately become empty, and thereby less 

 distinct when the worm is cut through its anterior part, but 

 subsequently, and in the posterior segments, the fluid cannot be 

 driven back from the tail towards the head by pressure, which 

 would be possible if there were a pulsating tube at the hinder 

 part. 



There is certainly no doubt that the vascular formation in the 

 head, especially as regards the anastomoses formed about the 

 suckers and rostellurn, differs according to the species. This can 

 be better explained by figures than by words. In order to study 

 the system of cephalic vessels, I recommend the reader to ad- 

 minister vesicular worms, and to kill the animal experimented 

 on from forty-eight to sixty hours after administration. With a 

 little pressure we then obtain with the microscope a very distinct 

 view, especially when the young Ttenice are examined in their proper 

 medium, that is, in a little intestinal mucus. The four lateral 

 longitudinal canals already mentioned are direct continuations of 

 the four longitudinal canals already existing in the scolex (head). 

 Besides these there is a system of very small, numerous capilla- 

 ries, although they may not be met with in the way represented 

 by Blanchard, after his injections. According to Wagener, 

 whose statements are confirmed by Meissiier, a considerable 

 number of small vessels, destitute of walls, issue from the larger 

 vessels, which possess proper walls. In both kinds of vessels, 

 especially in places where vessels communicate, ciliary formations 

 are observed, which, however, are wanting, according to him, in 

 the four vascular trunks ; these I think I have seen, at least at 

 the points where the smaller vessels open into the larger ones. 



