Japanese Freshwater Triclads. 



35 



ou 





to form an ana^^tomosing system. As is well known, the canals 

 make their way to the exterior at several points of the dorsal 

 surface, between the epidermic cells. Occasionally the two ducts 

 are seen to fuse together just before 

 opening out on the surface. 



Nervous System. — The exact ar- 

 rangement of the nervous system 

 could not clearly he ascertained. 

 The brain is a bilobed organ situated 

 near the anterior end of the body. 

 Each ])rain-mass gives rise to some 

 five forward ly directed sensory 

 nerves and some lateral nerves. 

 From the dorsal surface of the brain 

 the optic nerves arise and break up 

 into branches, extending to the 

 nunierous eye-spots. Each half of 

 the brain is continuous posteriorly 

 with one of the longitudinal nerve 

 cords, which themselves are rela- 

 tively thick. Throughout their 

 entire course, until they unite with 

 the marginal nerve at the posterior 

 end of the body, the two cords are 

 connected by numerous transverse 

 commissures, averaging about 55 in 

 number. Some of the commissures 

 are better developed than others and 

 these most frequently occur in tlie 

 neighbourhood of the pharynx- 

 insertion and the copulatory organs. 

 From the cords at points opposite to 

 tlie union of these with transverse commissures lateral nerves are 

 given off towards the marginal nerves. 



Genital Organs. — The common genital opening is situated 

 behind the mouth-opening at a distance equal to about one-third 



'>n — 



St' 



od'- - 



Text fi-f. 10. Diagrammatic re- 

 presentation of the organization of 

 Sorocelis safporo Ij. et Kab., as seen 

 from the dorsal side. 

 Index letters as in text figs. 2, 5 and 

 6. 



