288 ERNEST WARREN. 



distance below tlie oral sucker, aud it is produced from two 

 lateral plates of thick cells which appear at the place where 

 the embryonic gut-cteca come into contact (Fig. XI, 12 ; 



At this time the oral sucker is imperforate, but later the 

 fundament of the pharynx becomes connected with it by a 

 solid strand which ultimately splits and forms the mouth and 

 pre-pharynx. No oesophagus is formed until a much later 

 period after the animal has escaped from its cercaria-cyst. 



Gonads. — At this stage three compact masses of cells 

 become visible by reason of their great staining capacity; 

 the mass between the fundament of the cirrus-sac and the 

 ventral sucker will become the ovary, and the two larger 

 masses further behind of a somewhat elongated shape are the 

 embryonic testes (Fig. XIII, ov. and t.). Later on the testes 

 become globular, and the right-hand one becomes pushed 

 forwards. 



The genital atrium originates as a deep invagination of the 

 cortex at the anterior face of the depression of the ventral 

 sucker. Thus at first the genital atrium opens into the pit 

 of the sucker (Figs. XII, XIII, g. at.), but later it becomes 

 pinched off from it, so that in the adult the genital atrium 

 opens independently immediately in front of the sucker. The 

 embryonic genital atrium is lined by the general cuticle, 

 studded with spinelets. 



The fundament of the cirrus-sac and organs contained 

 therein, lying obliquely across the embryo, becomes narrow 

 at the right-hand end, bends sharply on itself, and extends 

 towards the genital atrium, but as yet it does not open into 

 it. This narrow portion Avill form the future cirrus and the 

 part of the sac immediately around it (Fig. XIII, c). 



A solid band of cells can now be found passing from the 

 ovary towards the genital atrium. This will become hollowed 

 out into a tube, and will form the oviduct, the uterus, and the 

 vagina (Fig. XIII, /. nt.). 



Clumps of large granular cells containing refringcnt 

 granules may be seen scattered about towards the posterior 



