14 THE INTERNAL PARASITES OF 



from Blanchard, shows the character well (Fig. 4) ; and 

 this lateral view of the parasite also permits us to recog- 

 nise the oral sucker, a, the large digestive tube of the 

 right side, b ; affording likewise a good general outline of 

 the water-vascular system, c, whose ultimate ramifica- 

 tions terminate in minute pouches. 



The development of the amphistomes is exceedingly 



Fig. 4. The Common Amphistome. 



interesting, not merely from a scientific point of view, but 

 as throwing much light upon the general question of the 

 origin and causation of fluke disease. A very closely- 

 allied species of amphistome resides in the frog, and we 

 have ascertained that its larvse either take up their abode 

 in, or dwell upon, the bodies of at least three different 

 species of water snails. The larval trematode is well 

 known to helminthologists under the title of Oercarea 

 diplocotylea. It measures about the twelfth of an inch 

 in length, and happens to be one of those cercarean forms 

 which is furnished with eyes. 



