4 



THE INTERNAL PAEASITES OF 



Flukes are very closely connected, structurally, with a 

 non-parasitic order of small creatures commonly inhabit- 

 ing ponds and ditches, and which are termed Planarians. 

 Some of these last-named creatures, however, dwell in 

 the sea, attaching themselves to rocks and weeds, crawl- 

 ing about after the fashion of leeches, to which animals 

 they bear a very general resemblance. They rarely 

 measure more than two inches in length. 



The planarians so nearly approximate to the common 

 liver-fluke in respect of their digestive organs that it is 

 well to understand this part of their structure. They 

 are extremely -voracious, being furnished with a compli- 

 cated stomachal apparatus. Look, for example, at this 



Fig. 1. A Planarian, showing the Digestive Organs. 



illustration of Eurylepta sanguinolenta (from Gregenbaur), 

 in which only the alimentary organs are displayed. You 

 perceive a rather large ventrally situated mouth (a), lead- 

 ing to a capacious gullet (b) ; whilst from the stomach 

 (c) there pass off numerous vessel-like branches, which 

 subsequently divide and subdivide, until at length they 



