Phyla Platyhelminthes and Nemertina 413 



duct of a human being. For excretion, there is a complex system of 

 flame cells at the ends of multibranched tubules. These smaller tubules 

 carry their wastes into two collecting tubes which empty into an excre- 

 tory bladder. An excretory pore is at the end of the bladder, near the 

 posterior portion of the body. 



Both male and female organs are present in the same individual. 

 There are two irregularly shaped testes located in the posterior part of 

 the body. From the testes, two vasa efjerentia pass anteriorly and join 

 to form the vas deferens. The vas deferens passes into a cirrus sac 

 near the anterior end ; this contains the seminal vesicle (an enlargement 

 of the vas deferens) for the storage of sperm, a mass of prostate glands, 

 and the cirrus or coptilatory organ. The cirrus may be extruded through 

 the genital pore which is common to both the male and female systems. 



The female system consists of the ovary and many associated ducts 

 and glands. From the ovary, a short oviduct leads to a bulblike en- 

 largement known as the ootype. Here are also found other ducts which 

 likewise enter the ootype. These ducts are a yolk or vitelline duct from 

 the yolk glands, a duct from the seminal receptacle, and Laurer's canal. 

 This latter canal leads to a dorsal pore and recently it has been dem- 

 onstrated that it may serve as a passageway for expelling excess 

 yolk. Surrounding the ootype is a cluster of glands, the Mehlis's 

 gland which may contribute to the production of the eggshell. The 

 yolk is furnished by a series of yolk glands or vitellary along each 

 side of the body. These are connected by small ducts to a single 

 large duct on each side which unites to form the common yolk duct 

 which enters the ootype. After the eggs are fertilized, they enter the 

 region of the ootype where the yolk is added, and the shell is put on. 

 When the eggs have been completed in the ootype, they enter the long 

 coiled uterus, which leads to the anterior genital pore. The distal por- 

 tion of the uterus may have special muscular walls. It is probable that 

 the sperm make their way through the uterus and the oviduct to fertilize 

 the egg. In some as many as 25,000 eggs a day may pass from a single 

 fluke. 



The Life Cycle of Opisthorchis Sinensis. — Throughout the 

 Orient, this is an important human parasite. The life cycle is com- 

 plicated, but quite similar to that of F. hepatica. The eggs escaping 

 from the infected individuals are eaten by snails, and within them, the 

 miracidium hatches and develops into sporocysts and rediae, reproducing 

 in the usual manner. The cercariae produced by the rediae escape from 



