■ENTOZOA. Entozoa. 
Entozoa.- 
303 
or four times, or even more. The anterior extremity 
is, in general, marked by several black specks arranged 
on each side of it, but variable in number. These are 
considered to be the eyes. The mouth is anterior, and 
almost always terminal, in the form of a slit, and for 
the most part provided with a protrusile, long proboscis. 
The intestine is simple, descending down the centre of 
the body in a straight or undulating line to the oppo- 
site extremity, where it opens outwardly by a pore 
similar to the mouth. The sexes are separate, and 
they multiply by ova, or perhaps, also, by transverse 
sections. The species are all marine, and are found 
living under stones and in mud between tide-marks. 
They appear to dislike the light, and prefer to live in 
obscurity. The species are very tenacious of life ; 
if cut into several pieces, each lives and moves, and 
perhaps each in time will grow up to a complete and 
perfect worm. Fresh water is a powerful poison to 
these worms ; if placed in a vessel of this fluid, the}' 
instantly show by their violent contortions how pain- 
ful and deleterious it is to them ; they soon breal? into 
pieces, disgorge portions of tbeir viscera, and speedily 
die and dissolve into a soft jelly. Some species pro- 
gress like the leeches, moving in great undulations from 
side to side, from right to left. All of them can creep 
up solid plane surfaces by means of contractions which 
sometimes change their general form in a very sin- 
gular manner. The number of males appears to be 
much inferior in proportion to that of females. As 
Quatrefages remarks, this is the case also with many 
of the intestinal worms ; in proportion, he says, as the 
organization of the lower animals becomes degraded, 
it appears that the female sex predominates more 
and more. 
Class — ENTOZOA (Intestinal Worms). 
As Siebold remarks, it is very difficult to characterize 
this class of worms, for it contains animals having 
widely dissimilar organization. Indeed this is so much 
the case, that some naturalists wish to suppress the 
class altogether, and it has been attempted to divide 
and isolate the orders amongst the various other classes 
of the inferior invertebrated animals. But such various 
difficulties have arisen from this, that in a work like 
the present it is much better to keep the class as a 
distinct one; for if we fail to perceive any common 
character in their organization, we can easily find one 
in their manner of living. The Entozoa are parasitical 
worms, which either during their whole life, or at least 
a part of it, inhabit the bodies of other animals, and 
derive their nourishment from them. 
The nervous system is feebly developed, and has 
only lately been distinctly recognized. In the majority 
it consists of two ganglia or two pairs, which unite 
together by a median band or narrow commissure, and 
give origin to two long cords which run through the 
whole length of the body. In some no vascular 
system has been recognized, but in others it is well 
developed. The circulating liquid, however, or blood, 
is in general wholly colourless. The digestive organs 
vary very much in the different orders. In some, as 
the Cestoid viorms and the Acanthocepliali, neither 
mouth nor alimentary canal have been observed — 
(Siebold); but in other orders it is pretty well developed. 
No respiratory system has as yet been satisfactorily 
observed. The intestinal worms, as their name im- 
ports, are almost all inhabitants of the internal parts of 
other animals ; there alone can they continue their 
species, and there alone can they obtain their nourish- 
ment. There is scarcely one animal that is exempt 
from these parasites ; and in general each genus seems 
to possess one or more species peculiar to itself, though 
often several species infest the different cavities of the 
same animal at the same time. For instance, there are 
about twenty distinct species that are found either in 
some of the cavities or in the muscular substance of 
man. They are most frequently met with in the 
alimentary canal, but they occur also in the cellular 
tissue, and in the parenchyma of the most closely- 
invested viscera, such as the liver and the brain. 
Though they are very frequent in diseased states of 
the viscera, and, when numerous, are the cause of 
disease themselves, they yet occur abundantly in per- 
fectly healthy subjects. Most of the Entozoa propa- 
gate by means of genital organs, which in some are 
situated upon a single animal, and in others upon two 
separate individuals. A few, however, multiply by 
fissuration, as is the case in the Tape-worms (Tcenid). 
The old opinion, therefore, that intestinal worms were 
products of spontaneous generation, is now completely 
exploded. It is exceedingly difficult, however, to 
conceive how these creatures can get into some of the 
obscure and well protected organs and parts of the 
body in which they are found. Not only the liver and 
brain, as mentioned above, but the lungs and blood- 
vessels are infested with them ; and it is affirmed they 
even occur in the unborn foetus. Some of the species, 
too, attain a large size ; and we must conclude that 
the germs from which they spring must be exceedingly 
minute, as they must be capable of being transmitted 
through capillary vessels and apertures too small to be 
discerned by the naked eye. 
The Entozoa differ very much from one another in 
form and organization, and, according to Cuvier and 
Professor Owen, have been divided into two large 
orders — I. Nematoid or Cavitary Entozoa (=Coelel- 
mintha — Owen ) ; those which have an intestine float- 
ing in a distinct abdominal cavity, commencing with a 
mouth, and terminating v.’ith a vent; II. Parenchy- 
matous Entozoa (=Sterelmintha — Owen ) ; those which 
have the viscera obscure, generally in the form of vas- 
cular ramifications, or even not discernible at all By 
this arrangement, however, worms the most dissimilar 
in their general appearance are grouped together, and 
a more natural method has been generally adopted. 
Rudolphi divides them into five orders, basing bis 
