194 UNSEGMENTED “WORMS.” 
development is afforded. The bladder is lost, and is of no 
importance, but the “head ” or scolex fixes itself to the wall 
of the intestine. There it is copiously and richly nourished, 
and buds off asexually a chain of joints. 
As these joints are pushed by younger interpolated buds 
farther and farther from the head, they become sexually 
Fic. 101.—Diagram of life history of Zenda soldum. 
First chapter: Tapeworm in man; #., head; PR., proglottides. Second 
chapter: Free proglottis and egg-cases; #7¢., uterus; ¢.a., genital aper- 
ture; embryo within the egg-case. Third chapter: Within the inter- 
mediate host, the pig; A., hexacanth embryo ; 4.sc., proscolex or bladder- 
worm; 2., muscle of pig; sc., scolex or head. 
mature. The ova are fertilised, apparently by spermatozoa 
from the same joint; the joint becomes distended with 
developing embryos. These ripe joints are liberated, the 
embryos are set free by rupture, and the vicious circle may 
recommence. Happily, however, the chances are many 
millions to one against the embryo becoming an adult. 
The above history is true, mez¢atis mutandis, for many other tape- 
worms. The embryo grows into a proscolex or bladder, which buds off 
