﻿30 MUSGRAVE. 



indefinite oval form. There are one or more suckers and in a few in- 

 stances one of these is armed with hooklets. The mouth or oral sucker 

 also performs the function of the anus. The cuticle in most species is in 

 part covered with scales or spines, but these are entirely absent in others. 

 The muscular system is rather poorly developed, it consists of a series of 

 fibers just beneath the cuticle and what is known as the parenchymatous 

 muscle, which sends branches throughout the body. A nervous system, 

 also poorly developed, consists chiefly of two or three ganglionic masses 

 near the head, with their corresponding trunks and branches to various 

 portions of the body. The digestive tract consists of a mouth (oral 

 sucker), pharynx, and oesophagus, which divides into two intestinal 

 caeca, which in turn, in a more or less winding manner, reach to the 

 posterior portion of the parasite and terminate as blind sacs. In the genus 

 Schistosoma there are one or more unions and separations of these in- 

 testinal caeca before they end in the posterior portion of the parasite 

 The excretory system is primitive, but fairly well developed. It begins 

 in excretory cells located in various parts of the body which lead by 

 channels with the usual anastomoses, to an opening in the posterior 

 portion of the parasite, called the excretory pore. The reproductive 

 S3 T stem is well developed and shows considerable variation in different 

 species. In the main, the prominent features are about as follows : 

 The two testicles are usually situated in the posterior portion of the 

 worm, and are of various shapes. Each one is connected by a seminal 

 duct with the vas deferns, which in turn passes forward and ends 

 in the cirrus pouch which is on the ventral surface and closely con- 

 nected with the genital pore. This pouch also contains the cirrus or 

 penis. From the vulvar opening the vaginal tube is continuous with 

 a well-developed uterus which usually has many folds and terminates 

 in the shell gland at the cotype. It is indirectly continuous through 

 the eotype with other tubes which also enter the latter as follows: The 

 oviduct which connects directly with the ovary, the vitelline duct which 

 is formed by tubes connecting with the yolk glands or vitelline follicles 

 and Laurer's canal, which is a small canal of unknown function opening 

 on the back of the worm and often distended at its inner end into a recep- 

 taculum seminis. Ova pass out through the vaginal outlet and at the 

 time of oviposition may or may not contain a ciliated embryo. In either 

 case, under proper environment, a ciliated miracidium escapes from the 

 egg and after a time enters an intermediate host. The parasite is 

 again taken into an animal host from some one of these unknown inter- 

 mediate ones and the adult parasite once more developes. 



The entire life cycle of any of these flukes with the exception of that 

 of F. Jiepatica Linn, is not known, but it is probable that the intermediate 

 hosts will be found among the same class of mollusks as the ones which 

 harbor F. liepatica. 



