THE WORMS 51 
first and scarcely showing the segments which finally be- 
come so prominent a feature. 
When carefully examined, a two-lobed brain is found 
in the “head,” and from it nerves extend the entire length 
of the body, followed throughout their 
course by the tubes of the excretory 
system ; also each segment contains a 
perfect reproductive system, so that 
even if it be separated from the others 
it may continue to exist for a consid- 
erable length of time. Furthermore, 
the tapeworms are surrounded by the 
predigested fluids of their host; a 
special alimentary canal is therefore 
superfluous, and all traces of it have 
disappeared. 
50. Development.—As the animal 
clings in this passive way to the body ANDES 
of its host the segments, loaded with Fic. 31.—Tapeworm (Twnia 
solium). In upper left- 
eggs ready for development, separate jana corner of figure is 
one after another from the free end _ the much enlarged head. 
of the body, pass to the exterior, and = ~“**" Tevosant- 
slowly crawling about like independent organisms, lay great 
numbers of eggs, which may find an intermediate host as in 
the life cycle of the liver fluke, and so in time find their 
permanent resting-place. Fortunately in all these parasitic 
forms, though an inconceivably great number of eggs are 
laid, only a comparatively few reach maturity. Even these, 
however, may cause at times great destruction among the 
higher, and especially our domestic, animals, often doing 
damage amounting to many millions of dollars per year. 
51. The tapeworm in relation to regeneration.—It has 
been known for more than one hundred and fifty years that 
some of the lower animals possess to a surprising degree 
the ability to regenerate parts of the body lost through 
injury. The Hydra, hydroids, and some of the jelly-fishes 
