106 Dr. Drummond on the Equivocal 
worms roll themselves up so pertinaciously by the action of 
their longitudinal muscles, that it is with the utmost difficulty 
the ends of the animal can be so straightened as to be di- 
stinctly seen ; and the muscles of the head and bothria in some 
species, as in several of the Bothriocephali, and particularly 
in the Scolex polymorphus, are in such perpetual activity, 
and cause so many changes of figure, that hours at the micro- 
scope are necessary before we can obtain a satisfactory know- 
ledge of the structure of the head. 
It so happens that some species have a much smaller mus- 
cular strength and activity than others, as, for instance, the 
Echinorhynchi ; and these might be readily carried through the 
alimentary canal of the animal in which they reside, had they 
their muscular power alone to trust to. And how does the 
clot provide for this? It forms a trunk or proboscis of ex- 
quisite workmanship, which it arms on all sides with sharp 
horny hooks; it forms muscles for the especial purpose of 
pushing out this proboscis, and others for drawing it in at 
pleasure into a sheath specially provided for it; moreover, 
this proboscis is so fashioned that it can be inverted or evert- 
ed upon itself, that is, it can be pushed out or retracted as a 
snail does its horn, without which second kind of motion it 
would be imperfect ; and thus by its twofold motion and its 
armament of rigid hooks, the proboscis is harpooned into the 
mucous coat of the intestine at the pleasure of the worm, 
which latter is thereby secured from removal by the pressure 
of the passing contents of the bowel. Some species, not con- 
tent with one proboscis, provide themselves with four, and 
these in some of the armed Bothriocephal present one of the 
most beautiful microscopic objects to be found in nature. 
But the work is not yet complete; sensation is further 
wanted. We are to suppose, that as the animal has acquired 
a digestive apparatus, it has superadded to this the sense of 
taste ; but at all events it has the sense of touch, and therefore 
has provided for itself a system of nerves ; for without a ner- 
vous system in some form or another, none, I presume, will 
insist that there can be sensation. With regard to the sense 
of smelling I say nothing; and persons who consider such 
subjects, would perhaps be of opinion that the entozoic life 
would be as comfortable without as with that sense. But as 
respects seeing, since organs of vision would be altogether 
superfluous in habitats where midnight darkness holds per- 
petual reign, we find accordingly that in no instance have the 
Entozoa provided themselves with eyes. 
Let us next suppose that the clot, which has thus so mar- 
vellously metamorphosed itself into an entozoon of admirable 
