536 
transparency and smooth surface, and under 
the highest powers of the microscope present 
neither an appearance of cross markings nor 
of a linear arrangement of globules.” Besides 
the retractor muscles in the Bryozoa there like- 
wise exists a muscular membrane which lines 
the cell, and forms the parietes of the body, 
in which fibres are distinctly apparent, running 
transversely: these by their contraction com- 
ing the visceral cavity and the fluid which 
it contains will tend to elougate the body of 
the Bryozoon, and assist in effecting its protru- 
sion; although, as Dr. Farre supposes, this 
process is principally accomplished by the 
cooperation of the alimentary canal, which has 
the power of straightening itself from the sig- 
moid flexure, into which it is thrown when the 
animal is retracted. 
The condition of the nervous system in the 
Bryozoa has not been as yet made out, a cir- 
cumstance at which no one will be surprised 
who considers the extreme difficulty of micro- 
scopic researches concerning the structure of 
animals so minute as these ; but from the close 
affinity that there decidedly is between these 
animals and the Rotifera, there can be little 
doubt that a similar arrangement exists in 
both. 
Inthe Rorrrera or Wheel Animalcules, the 
nervous system, according to Ehrenberg, con- 
sists of several filaments communicating with 
minute ganglia dispersed in different parts of 
the body, although without any obvious arrange- 
ment or symmetrical disposition, so that the 
muscular apparatus in these beautiful animals 
dienes itself in a very perfect state of deve- 
opement. The ciliated organs around the 
mouth, which are apparently the representatives 
of the ciliated arms in the Bryozoa, are retracted 
by a special set of muscles derived from the in- 
terior of the membrane that lines the shel! and 
circumscribes the visceral cavity, and the antago- 
nists to these are the delicate parietes of the 
visceral cavity itself, which acting upon the fluid 
therein contained, causes the extrusion of the 
ciliated lobes, whenever the wheel-like organs 
are required to be put in motion.* 
But besides the muscular bands, that, in 
the Rotifera, are appropriated to the protrusion 
and retraction of the wheel-bearing organs, 
others are connected with a peculiar prehensile 
apparatus placed at the hinder extremity of the 
body, and forming an instrument of very great 
importance in the economy of these creatures. 
It consists of a prehensile forceps, the blades 
of which are worked by distinct muscles; and 
by the assistance of this organ the action of the 
wheel-like cilia is at once changed from that of 
a locomotive power into a means of procuring 
and seizing food. If these forceps are not 
* It seems more than probable that the tranverse 
muscular fibres that occur in the parie.al membrane 
of the Rotifera have been mistaken by Ehrenberg 
for vascular canals, described by tha. observer as 
emanating from a dorsal vessel; such at least is 
the opinion of Dr. Arthur Farre in the memoir 
above referred to, an opinion which quite coincides 
with the result of our own observations upon this 
subject. 
MUSCULAR SYSTEM. 
employed, the apparent! ee ae = 
pe the little weit rapid through the water; 
t does it choose to take hold of some foreign 
body by means of its forceps, and thus anc 
itself in a given spot, the use of the whee 
entirely changed, their rotation merely 
ducing currents or rather a powerful whirlpool 
in the water, which sucks from a distance every 
thing within its influence, and thus brings food — 
into the mouth. ~ 
The next class of animals, the Ep1zoa, pre=_ 
sent us with a beautiful series of gradation 
development, clearly demonstrating the insepara 
ble relation that must exist between the nervot 
and locomotive systems. The Epizoa see 
indeed, to be the osculant group interpe 
between the Intestinal worms ps the vt 
lated classes, and exhibit in a permanent con-— 
dition the progressively improving external 
articulated limbs, which are we permitted to 
attain their full development in higher races of 
the animal creation. The Epizoa, like the 
Ceelelmintha, are parasitic in their habits, livin: 
however, upon the external surface, and not in 
the interior of other animals. They are prin= 
cipally found fixed to the eyes, the skin, the 
gills, or even the inside of the mouth of fishes 
or to the branchial organs of various forms of 
aquatic animals, from which they suck thi 
materials necessary for their support, and at | 
same time are freely ex to the influences 
of the surrounding medium for the purpose 
respiration. In the humblest of these parasite 
the structure of the body is scarcely supe! 
to that of many Ceelelmintha, suckers and pre 
hensile organs placed in the vicinity of th 
mouth being their only means of adhering to th 
surface upon which they live; but in the Le 
neans the first appearance of outward liml 
begins to be perceptible, not as yet recognisabl 
as legs or locomotive agents, but not the I 
on that account the first rude sproutings ¢ 
members that are to be by degrees perfected” 
more highly privileged genera. Some of the 
Lerneans, indeed, present most grotesq) 
shapes, and a!most exactly resemble the e 
bryos of Vertebrate animals at the period wh 
the first buddings of limbs begin to pro, 
from the sides of the body. This resemblat 
indeed, is far more real than it would at 1 
appear, inasmuch as there is a parallelism 
be established between the permanent coi 
tion of the Lernean and the transitory stat 
the embryo at the corresponding 0 
development that is strictly physiological. — 
condition of the nervous system in them 
is precisely similar, exhibiting in both ¢ 
the nematoneurose type; the same rudi 
tary condition of the muscular system is 
sequently equally met with in the embry 
in the Lernean, but as the nervous syste 
the former is rapidly advancing to a | 
exalted state of development, so do the 
and the muscles appertaining to them impr 
in the same ratio. = 
In the higher genera of Ep1zzoa mi 
ganglia exist in connexion with the ner 
filaments, and in such the limbs are of e¢ 
more exactly formed and begin to sketel 
