TREMATODA. 777 



them in the grass where they have fallen, and also, pro- 

 bably, aid in the further expulsion of eggs, which latter 

 can only pass from the oviduct in single file, one at a 

 time. 



5. After the death of the escaped flukes, the further dispersion 



of the eggs is facilitated by the subsequent decomposi- 

 tion of the parent worm, and also by its disintegration, 

 occasioned by the attacks of insects. It has been calcu- 

 lated that the uterus of a full-grown fluke may contain 

 upwards of forty thousand eggs. 



6. By the agency of winds, rains, insects, the feet of cattle, 



dogs, rabbits, and other animals, as well as by man 

 himself, the freed ova are dispersed and carried to con- 

 siderable distances ; and thus it is that a considerable 

 proportion of them ultimately find their way into ponds, 

 ditches, canals, pools of all kinds, lakes and running 

 streams. 



7. The eggs at the time of their expulsion exhibit the already 



segmented yolk in a state of fine division. The egg 

 contents continue to develop outside the parent's body ; 

 the granular matrix finally becoming transformed into a 

 ciliated embryo, which, when set free, follows the habit 

 of infusorial animalcules in general by swimming rapidly 

 in the water. The escape of the embryo is efiected at 

 the anterior pole of the egg-shell, which is furnished with 

 a lid that opens in consequence of the action of prolonged 

 immersion, aided by the vigorous movements of the con- 

 tained embryo. 



8. The ciliated, free, swimming embryo of the common fluke, 



at the time of its birth, exhibits the figure of an inverted 

 cone, its anterior extremity, which is broad and some- 

 what flattened, supporting a central proboscis-like papilla. 

 A small pigment spot, placed dorsally, and having the 

 form of a cross, is supposed to be a rudimentary organ of 

 vision. After the lapse of a few days the cilia fall off, 

 the embryos then assuming the character of planaria-like 

 creeping larvae. 



