446 
REMARKS ON ENTOZOA. 
manufacture taeniae or coenuri at pleasure from each other, 
either being given as the starting point. The coenurus is the 
only animal of the kind which has been experimented upon, 
but doubtless others of the group would behave in the same 
manner. In fact, something of the same nature has been 
observed to occur with the cystercus rattus, a hydatid infesting 
the liver of the rat ; for -when devoured by the cat, the cys- 
tercus becomes a taenia in its intestines. And again, tania 
serratus has been developed in dogs by feeding them on the 
cystercus pisiformis of rabbits. The difference between the 
cystercus and coenurus consists merely in the peduncular 
organs and heads being reduced to one ; and both these entire 
animals resemble the head and anterior segment of the tape- 
worm, except in so far as they are destitute of generative 
organs and a nervous system. 
By the discovery of these affinities, the study of the 
entozoa becomes much simplified. The cystercus and cystic 
animalculae appear to be the forms which the entozoa assume 
when found infesting tissues, w r hile the taeniae are produced 
from the same germs when lodged in the intestinal cavity . 
According, then, to the situation of the germ, cystics or 
cystercians, or tapeworms, are developed. 
The greatest difficulties, however, are to account for the 
germs of the animalcules reaching the body, and for their 
developing themselves in certain situations in preference to 
others. Now the ova of these animalcules are very minute. 
The cellular germs may, for example, be scattered about on 
the grass or fields, where rabbits affected with cystercus pisi- 
formis sport, or where dogs affected with tape-worm wander, 
and these germs may thus readily reach the outlets of the 
bodies of sheep or other animals which feed there. From 
their minuteness (for they are, we believe, as small as pus- 
corpuscles or blood-globules), they will readily transude 
through the w r alls of the blood-vessels, and enter the 
system. Once there, they will be passed on by the blood 
till the u elective affinity” of a certain part of a tissue attracts 
them to itself in the same w r ay as it draw s to itself the parti- 
cles of nourishment which alone can form its substance — in 
the same way as certain tissues attract the elements of a 
disease w hich never affects any but themselves— in the same 
w ay as the liver or the mammary gland attracts the cancerous 
germs which circulate in the blood. This is, however, pro- 
bably not the only modus operandi in the occurrence of 
entozoa, for their ova may sometimes be deposited mecha- 
nically. For example, in the production of intestinal worms, 
it is not necessary that the ova should be first absorbed and 
