CESTODA. 



247 



the head and the suckers. An alimentary canal is also wanting. 

 The nutritive fluid, already prepared for absorption by the host, 

 passes endosmotically through the body-wall into the parenchyma. 



The excretory apparatus, on the contrary, attains a considerable 

 development as a system of much ramified canals which are distributed 

 throughout the whole body.* It consists primarily of two longi- 

 tudinal canals (a dorsal and a ventral f), running along each side of 

 the body and connected in the head and in each segment by trans- 

 verse trunks (Figs. 198, 199). According to the state of contraction 

 of the muscular system these longitudinal trunks and cross branches 

 appear sometimes straight and some- 

 times bent in a wavy or zigzag 

 manner : their breadth also presents 

 considerable variation, so that the 

 power of contraction has been 

 ascribed to their walls. The longi- 

 tudinal trunks only serve as the 

 efferent ducts of a system of very 

 fine vessels which ramify through- 

 out the whole parenchyma and 

 receive numerous long tubes : the 

 latter begin in the parenchyma with 

 closed funnels, which contain a 

 vibratile ciliated lappet (Fig. 200). 

 The larger vessels are said to con- 

 tain valves. In many cases, as in 

 Ligula and Caryophyllaeus, these 

 longitudinal trunks are broken up 

 into numerous longitudinal vessels, 

 which are connected by transverse 

 anastomoses. In other cases, on the 

 other hand, the two ventral vessels are enlarged at the cost of the 

 two dorsal, which may entirely atrophy. The external opening of 

 the excretory system is, as a rule, placed at the posterior end of the 

 body, i.e., at the hind end of the last segment, in which a small 

 vesicle with an external opening receives the longitudinal trunks. 

 According to the observations of Leuckart on Taenia cucumerina, 

 the posterior transverse canals in the segments immediately preceding 



* Compare Th. Pintner, " Untersuchungen iiber den Bau des Bandwurm- 

 korpers," Wien, 1880. 



t These surfaces are distinguished by the generative apparatus (see below). 



FIG. 200. A portion of the excretory 

 system of Caryophyllaeus mutabilis 

 (after Pintner). Wb ciliated funnels 

 with the nucleus of the cell belonging 

 to them. 



