138 NEW YORK ZOOLOGICAL SOCIETY: 
which contain both male and female generative organs. As 
these segments or proglottides are pushed by younger interpo- 
lated buds further and further from the scolex they become sex- 
ually mature, developing complex hermaphrodite reproductive 
organs. The ova produced in these are fertilized apparently by 
spermatozoa from the same proglottide. As each segment be- 
comes perfect it produces a vast number of eggs, and finally 
drops away from the main colony. The ova, or eggs, contained 
within each segment may be expelled within the host or may not 
be released until the segment is outside the body. 
The proglottides, after separation from the main colony, con- 
tinue to live for some time independently, and may increase in 
size considerably if they remain in the body of their host. After 
it is cast off and reaches the exterior it retains its vital power 
for a short time, and has been known in some instances to crawl 
a considerable distance, leaving in its wake a yellowish trail com- 
posed of eggs escaping from a rupture in the body wall. The 
proglottis soon dies, however, and decomposes, the eggs are scat- 
tered, but they soon lose their vitality in a dry atmosphere. 
The eggs are round or oval in shape, and very small, consisting 
of a minute ovum embedded in yolk cells, and surrounded by a 
thin membrane. Unless these eggs are taken into the body of 
herbivora by drinking contaminated water, or by eating grass 
or herbage with the eggs deposited on it, they quickly perish. 
If a segment is eaten it is digested, and the ova or eggs are 
liberated, but if the eggs only are eaten the egg membranes are 
digested by the gastric juices, and the embryo is set free. 
Each embryo is provided with six hooklets, and as soon as 
set free begins to bore its way into the gastric or intestinal vessels 
by means of its hooks. 
MIGRATION OF THE EMBRYO 
is said by some to be voluntary, by others to be involuntary ; 
but when they are once within the vascular channels they are 
carried along passively, doubtless, until reaching a position where 
the embryo finds in certain parts of the organism the conditions 
necessary for its development and growth. 
The vesicle gradually becomes a cystic worm by the forma- 
tion of a hollow ingrowth, which is developed from the walls 
and projects into the interior of the vesicle. The suckers and 
circlet of hooklets are formed on the inside and at the bottom 
