Japanese Freshwater Triclads. /^\ 



posterior trunk is usually provided with 10-17 l)rariclies, those 

 inwardly directed being either very small or, as is frequently the 

 case, joining together the two trunks. 



Excretory System,. — So far as I liave observed, there are two 

 main vessels on the dorsal side of the body, extending almost 

 throughout the whole length. They are connected with eacli otlier 

 by means of anastomosis. The canals make their way to the 

 surface in the usual manner. 



Nervous System. — Each longitudinal nerve cord passes forward 

 over a well-developed brain-mass, those of both sides being con- 

 nected by some transverse commissures. The foremost commissure 

 is the most developed of all of them. From each ))rain-mass arise 

 some five forwardly directed sensory nerves excluding the optic 

 nerve, and some lateral nerves. Throughout their entire course 

 the longitudinal cords are connected by numerous transverse com- 

 missures, and give off lateral branches of the same number. 



Genital Organs. — The common genital aperture is placed near 

 the middle of the posterior third of the body. It leads into the 

 atrial cavity which is divided into two chambers, the penis- 

 sheath and the vestibulum, separated bj^ a tubular diaphragm of 

 muscular nature. Its free end is retro versed into the penis-sheath. 

 Doubtless the penis appears to extend through the lumen of that 

 body to the exterior. This organ is covered with an epithelium 

 continuous with the lining epithelium of the atrial chamber. The 

 numerous glands, which are embedded in the surrounding paren- 

 ch3^ma, open out on the internal surface of the diaphragm and 

 partly on the surface of the vestibulum. The sphincter muscles of 

 the diaphragm consist of three sets of fibres, circular, longitudinal 

 and radial, of which the radial fibres are present in a stiongly 

 developed condition. The penis-sheath is provided with a 

 muscular wall continuous with that of the penis and thickest on 

 the dorsal side. There can be distinguished two sorts of circular 

 and longitudinal muscular fibres, of which the longitudinal 

 muscles are developed to an extraordinary degree. 



The testes number about 19-21 on either side of the body, 

 occupying a ventral position on each side of the anterior gut trunk 



