Dr. Drummond on the Equivocal Generation of Entozoa. 101 
the motions of the animal are in the highest degree slow and 
sluggish, which I have likewise observed in fs Aes ee Oculina 
and Cladocora. 
Priate IV. Fig. 6. Desmophyllum Stellaria, Ehrenberg. Nat. size, sitting 
on Nullipora Lithophyllum expansum, Phil. 
XV.—Thoughts on the Equivocal Generation of Entozoa. By 
| Jas. L. Drummonp, M.D., Professor of Anatomy and 
| Physiology in the Royal Belfast Institution, &c. 
In studying the Entozoa, one of the first things which de- 
mands our attention, is the peculiarity of the situations which 
they occupy. When we look abroad upon the features of the 
globe which we inhabit, we find that every part is filled with 
animal and vegetable life; whether we visit the frozen regions 
of the poles, or the countries for ever exposed to the heat of an 
equatorial sun, we see that every clime has its animals and 
plants, and these in general, so constituted in their structure 
and ceconomy, as to be fitted peculiarly for the circumstances 
of the place in which they reside. The White Bear delights 
in the perennial snows and ice of its native region, and the 
Lion in the fervour of the torrid zone ; but were they to change 
situations, the former would die from the excessive heat, and 
the latter would as certainly perish from the intolerable cold. 
And so it is with the Entozoa; they have been ordained 
to inhabit, alone, the interior of other animals; and though 
many of them will live for several days when removed from 
that situation and put in water, yet that can only be deemed 
a lingering death, for at length they infallibly perish from the 
unnatural circumstances in which they are placed. It has 
been asserted, indeed, that some of the intestinal worms 
have been found living in other situations. Thus, Linnzus 
supposed that the Fluke-worm (Distoma hepaticum) was to 
be found in fresh water, as also the common T'ape-worm in 
muddy pools, and the Ascaris vermicularis in marshes among 
the roots of decaying plants. (Rudolphi, i. 371.) But it has 
been shown by Muller and Rudolphi, that he had mistaken 
other external species of animals for true Entozoa; that his 
supposed Tenia and Fluke-worm were the Planaria lactea, 
and his Ascaris vermicularis a quite different animal. 
But even admitting that a true entozoon should be found in » 
a pool or rivulet of fresh water, still something more would be 
necessary to prove that such was its natural habitat. Every 
one knows that when an animal is infested with Tape-worm, 
portions of the latter are ee ejected ia Ww ith the 
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