GENERAL REMARKS 235 



In the whole length of the body placed laterally. 



They are always small and numerous. 



Laurer's canal is on the dorsum and is for the escape of yolk food 

 when it is in excess, thus preventing the uterus being blocked with 

 volk (Leiper). 



THE LIFE-HISTORY. 



This is taken from a known typical example, viz. : Fasciola 

 he pa tic a. 



The ovum passes along the ovarian duct from the ovary and in 

 this tube is fertilized and surrounded by yolk cells. 



The shell gland then secretes a shell around the mass w'hich then 

 passes to the uterus and escapes in the faeces of the parent worm. 

 The egg thus passed has a lid. (Except the Schistomidse.) 



The ovum segments and grows, using up the yolk and forms a 

 Miracidhim. This escapes in a few weeks from the lid of the egg into 

 the water. It has two eye spots, anterior papillae and cilia by which 

 means it swims about. It now grows and develops an alimentary 

 canal. By means of its anterior papillae it enters the cavity of some 

 snail, otherwise it dies in about eight hours. The special organs are 

 now lost. The organism grows and a sporocyst is formed. Cellular 

 differentiation again takes place. 



The organism now has a cuticular lining, under which is a muscular 

 layer lined with epithelium internally, forming thus a cavity which 

 answers as an alimentary canal. This form is the redia. It now- 

 forces its way out of the cyst and wanders about the snail. It has a 

 ridge or collar about its anterior end, and two stumpy protuberances 

 posteriorly to aid locomotion. 



Cells now bud off from the inner side of the body wall forming the 

 cercaria. This is something like a young Fasciola with a tail. 



These cell groups pass out from the redia by the genital pore, 

 then leave the snail, swim about in the water, become encysted on 

 grass and water weeds, and are then devoured by sheep, &c. In the 

 process of ingestion they lose their cyst, travel to the bile ducts, and 

 there develop into mature flukes in about six weeks. It will be noticed 

 that many flukes develop from one egg. 



HABITAT. 



They occur in the liver, intestines, lungs and urinary tract of man. 



Dogs, pigs, cats and cattle are also infected. 



In sheep they cause what is commonly known as " sheep-rot." 



They may not cause obvious symptoms in man, but there may be 

 irritation of any of the above organs by the eggs or the parasites 

 themselves. 



Sometimes thev cause serious diseases in man. 



