LIFE-HISTOEY 31 



e. The oviduct, or ' uterus,' formed by the union of 



the ovarian and vitellarian ducts in the midst of 

 the shell-gland, is a wide much-convoluted tube 

 lying between the shell -gland and the genital 

 aperture. Its convolutions extend half-way across 

 the animal, and numerous eggs can be seen 

 within it, 



f. The aperture of the oviduct is at the base of the 



penis, and on its left side. When the penis is 

 fully withdrawn a slight cavity, the ' genital 

 sinus,' is formed, into the left side of which the 

 oviduct opens. 



E. The Nervous System. 



This cannot be made out with certainty in specimens 

 prepared as above. It can be seen in a specimen rendered 

 transparent by caustic potash, though such preparations are 

 very perishable : and it may also be made out in sections. 



It consists of a nerve-collar around the pharynx, with two 

 lateral ganglia and a median ventral one. From these arise 

 nerves, of which two large lateral ones are the chief. These 

 two run backwards, one on each side of the body (fig. 6). 



II. LIFE-HISTOEY OF THE LIVEE-FLUKE. 



The development of the liver-fluke can only be studied 

 under very special conditions. 



The main features in its life-history, as determined by 

 Professor A. P. Thomas, are as follows. 



A. The First Generation is produced sexually but is itself 

 asexual. 



1. The eggs, laid in large numbers in the bile-ducts of the 



sheep or other infected mammal, pass with the bile 



into the intestine, and so escape from the body. 



They are ovoid bodies, '13 mm. long and -08 mm. 



broad, enclosed in smooth brownish chitinous shells. 



Within each shell are a single germ-cell and a large 



