TENIA. 343 
This worm is occasionally found in children, and less often in adults. The * 
reason assigned for its greater frequency in the former is their more intimate 
relation with the dog and cat, it being thus implied that they become infested 
through those pets. 
Tania Echinococcus is the smallest tape-worm found in the dog. It is 
about one-fourth of an inch in length, and usually made up of three seg- 
ments, including that of the head, but occasionally there are four. The term 
‘‘hydatid” is applied to the larval or bladder-stage of this parasite. The 
fertilized eggs are contained in the last segment, which in time softens and 
disintegrates. If, after being discharged from the intestines of the dog, these 
eggs, either free or still in their segments, enter the stomach of a suitable ani- 
mal, their thick fibrous capsules or shells are digested by the gastric juice, and 
Tenia Cucumerina, natural size. (Von Siebold.) 
thus the embryos are set free. All are provided with six hooklets, with which 
they attach themselves to the walls of the stomach. Through them they bore 
with ease. They are believed to sometimes enter the liver by way of the bile- 
ducts; but generally they are carried through the blood-vessels and lymphatics 
to different parts of the body, and especially to the internal organs. Finally 
stopping, they undergo further development by a process of growth and 
metamorphosis into the characteristic bladder-cysts, which may be as small 
as a pin-head or as large as the head of a child. In its strobila condition this 
parasite is said to infest only dogs and wolves. The former are regarded as 
practically the one source of hydatid disease. Certainly their opportunities 
of becoming infested are good and constant. It is also a notable fact that the 
extent of the hydatid disease depends very largely upon the number of dogs in 
the community. Besides harboring mature tape-worms of this species, the dog 
may serve as an intermediary host and convey the ova to man. The eggs may 
