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 with 
other 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 flesh food. The entozoon in question is 
the margined tapeworm. This worm (7enza marginata) 
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 
NCWIT Cede 
a ee 
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 
