TREMATODA 



133 



O.s 



N.ph. 



M.I. 



In the NERVOUS SYSTEM (fig. 68) can be distinguished a cerebral 

 portion as well as fasciculi (usually termed nerves) running from 

 them, and peripheral nerves. The cerebral portion always consists 

 of two large ganglia situated in the anterior end of the body 

 which pass dorsally over the oesophagus and are connected by 

 means of a broad and 

 thick commissure com- 

 posed of fibres only. 

 From each ganglion three 

 nerves project towards 

 the front the inner and 

 dorsal nerve for supply- 

 ing the anterior dorsal 

 part of the body ; the 

 median and ventral for 

 the oral sucker : and the 

 exterior and lateral like- 

 wise for the supply of the 

 sucker. 



In a similar manner 

 three fasciculi proceed 

 backwards from each 

 ganglion, one dorsal, one 

 lateral and one ventral. 

 The dorsal and ventral 

 fasciculi become united 

 and curve backwards ; 

 the symmetrical lateral 

 fasciculi are connected by 

 means of transverse com- 



G.p. 



E.xp. 



FIG. 68. Harmostomum leptostomum (Olss.) 

 in its immature condition (from Helix hortensis}. 

 missures, the number Ot Nervous system, according to Bettendorf, mag- 

 ;VirTi varv irrorrHnp- to nified : A ' s " Abdominal sucker; C.g., cerebral 

 Which \ary aCC ganglion; Ex.p., excretory pore; G.p., genital 



the species. Such com- pore ; O.s., oral sucker ; M.d., dorsal medullary 

 -, v fasciculus ; M.I., lateral medullary fasciculus ; 



missures also exist N ^ pharyngeal nerve . MmVtt ven trai medui- 



tween the lateral and the lary fasciculus. 

 two other fasciculi on each 



side. There are ganglion cells along the entire course of the pos- 

 terior cords, more particularly at the points of departure of the 

 commissures. There also appears to be in addition a fourth an- 

 terior and posterior pair of nerves, the front pair for the oral 

 sucker and the hind pair for the pharynx. 



The peripheral nerves, which spring from the % posterior cords 



