Internal Parasites. 229 



plunge into an ordinary field pond to wash himself, such 

 an act conveys numerous eggs into the water ; and the 

 next herbivorous animal that comes to slake its thirst will 

 be liable to drink in one or more of the parasites' eggs. If 

 thus the hogget or a calf swallow the eggs of a gid-tape- 

 worm, " turnside" will be the consequence ; but if the her- 

 bivore swallows the eggs of the hydatid tapeworm, properly 

 so-called, hydatids will be the result. And so on vvith 

 otter creatures which happen to ingest the ova of different 

 and appropriate parasites. 



To hares and rabbits the dog thus communicates another 

 bladder-worm disease ; and we ourselves are also liable to 

 become infested with hydatids from the same source. 



Another parasite of this class is described as follows by 

 Dr. Cobbold : " The largest tapeworm liable to reside in the 

 dog is a parasite chiefly derived from the sheep ; that is to 

 say, the sheep acts as the principal intermediary bearer of 

 the larval cestode, which latter acquires tapeworm maturity 

 when it is taken into the stomach and intestines of the 

 dog along with ilesh food. The entozoon in question is 

 the margined tapeworm. This worm {Tcenia marginatd) 

 reaches a length of from five to eight feet. It is an abun- 

 dant species, occurring, probably, in fully 25 per cent, of 

 English dogs that are not less than one year old. In 



FIG. 28. 

 LARVA OF THE MARGINED TAPEWORM. (gOEZE.) 



Denmark it occurs in 14 per cent. ; and in Iceland, ac- 

 cording to Krabbe, in no less than 75 per cent, of the 



