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been discovered in the guinea pigs, though they have very 
frequently been sought after in those animals. 
Among vertebrated animals, the entozoa are in general 
more common and more numerous in the aquatic species 
than in the others ; more so in the females than in the males; 
more so in the young than in the old; and, finally, more so 
in weak individuals than in vigorous subjects. 
It has been for a long time admitted in a general way, that 
each intestinal worm more peculiarly infests some one ani- 
mal, and even a determinate part of that animal; but this 
opinion can by no means be supported in any positive man- 
ner. In fact, it is certain that the asearis lumbricoides, for 
example, is found in the human species, in the horse, the pig, 
and some other animals. — It is equally proved that the same 
species of tenia is to be found in the cat and in the dog. 
Nor are we less assured that the bothryocephalus punctatus 
is to be met with in the barbel, the turbot, and several other 
species of pleuronectes. 
Nevertheless, there are some species which are evidently 
peculiar to some particular species of mammifera, such as the 
human tzenia and the bothryocephalus. 
Locomotion in these animals is but seldom, even slightly 
extended, and a certain number of them do not possess the 
faculty at all, but remain fixed in the parts in which they 
live. These, then, are strictly parasites, altogether fixed, as 
are the echinorhynchi, and the majority of the tznioides. 
There are only, in such cases, some partial movements, or a 
sort of undulation in those parts of their bodies which are not 
adherent. It is not the same with several other species, such 
as the ascarides, and even the porocephali, in which there is 
a true general locomotion, or total transport of the body, in 
the parts which they inhabit, for it is certain that the asca- 
rides lumbricoides, whose normal position is in the small 
