356 ZOOLOGY. 



by a short oesophagus into a bifurcated intestine, each 

 branch of which extends nearly to the posterior end of 

 the body. There is no anus or aperture to the intes- 

 tinal cavity except the mouth. Each main branch of 

 the intestine gives off numerous lateral diverticula, those 

 on the inner side towards the middle line being short and 

 simple, those on the outer side longer and branched. 

 Thus the various ramifications of the intestinal cavity 

 extend through all parts of the body. 



The nervous system consists of an anterior nerve collar 

 encircling the pharynx, having a ganglion on each side 

 and one ventral. From each lateral ganglion there passes 

 a ventral nerve cord to the posterior extremity of the 

 body. 



The excretory organs consist of a paired system of 

 tubules communicating with a median duct in the 

 posterior two-thirds of the body. This duct opens by a 

 pore at the posterior extremity. The branches of this 

 duct break up into numerous ramifications, which extend 

 into all regions of the body. The ultimate tubules take 

 their origin in cells which are enlarged and hollow, and are 

 provided internally with one or more long cilia or flagella, 

 the undulating motion of which suggests the flickering of a 

 flame, whence the cells are called flame-cells. The function 

 of these vibratile flagella is to cause a current in the liquid 

 secreted by the flame cells and tubules towards the efferent 

 ducts. The tubules appear to be intracellular, like that of 

 the nephridium in the earthworm. 



3. Generative Organs. The animal is hermaphrodite 

 and the generative organs are complicated. Like the other 

 systems of organs, they extend into all parts of the body 

 (fig. 186). The female system consists of vitelline or yolk 

 glands, ovary, shell-gland, and uterus. The vitelline glands 

 are very small and very numerous, and are situated in the 

 lateral regions on each side of the body. Each gland has its 

 own duct, and the various ducts unite together to open into 

 a longitudinal duct on each side. From each longitudinal 

 duct passes a transverse duct a little behind the ventral 

 sucker, and the two transverse ducts unite together and 



