328 



PLATYHELMIXTHES. 



The nervous system consists of two lateral longitudinal cords passiug 

 externally to the main trunks of the excretory system. They are 

 somewhat swollen in the head, where they are connected by a trans- 

 verse commissure; these anterior swellings and the commissure 

 may represent a cephalic ganglion. Distinct sense organs are 

 wanting, but the tactile sense may be ascribed to the skin, especially 

 to that of the head and the suckers. An alimentary canal is also 

 wanting. The nutritive fluid, already prepared for absorption, 

 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 dis- 

 tributed throughout the whole 

 body.* It consists primarily of 

 two longitudinal canals (a dorsal 

 and a ventral), running along each 

 side of the body and connected in 

 the head and in each segment by 

 transverse trunks. According to 

 the state of contraction of the 

 muscular system, these longitudinal 

 trunks and cross branches appear 

 sometimes straight and sometimes 

 bent in a wavy or zigzag manner : 

 their breadth also presents consider- 

 able variation, so that the power of 

 contraction has been ascribed to 

 their walls. The longitudinal trunks 

 only serve as the efferent ducts of a 

 system of very fine vessels which 

 ramify throughout the whole paren- 

 chyma and receive numerous long 

 tubes : the latter begin in the 



Fio. 261. A portion of the excretory 

 system of Cari/opJiyHceus mntabilis 

 (after Pintner). Wb, Ciliated funnels 

 with the nucleus of the cell belonging 

 to them. 



parenchyma with closed funnels, which contain a vibratile ciliated 

 lappet (fig. 264). In many cases, as in the Ligididce and Caryo- 

 f>liyUcPus t 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 



* Compare Th. Pintner, " Uutersucbungen iiber den Bau des Bandwunn- 

 korpers," Wien, 1880. 



