We need scarcely say that in the Agastrica 
no muscular system whatever can be detected, 
the living portions of their bodies being entirely 
made up of a soft granular parenchyma which 
only dubiously exhibits contractile movements 
under any circumstances. 
group of animals naturally allied to each other 
in the general details of their economy, but 
offering very great diversity of structure and 
external form. In the simplest or gelatinous 
Polyps ( Hydride) the acrite condition of the 
nervous and muscular tissues is most conspicu- 
‘ously exemplified. Examined under the mi- 
‘eroscope, the entire substance of the minute 
gelatinous bag composing the body of the 
Hydra seems to consist of a glairy material, 
_ wherein are suspended coloured globules that 
constantly change their relative pesitions, and 
_ move about from place to place as the creature 
contracts, or extends different parts of its sub- 
Stance, but not a fibre or filament is discernible 
Passing in any direction, nevertheless the move- 
‘ments of the Hydra appear to be performed 
with facility, and its powers of locomotion are 
considerable. 
__ In the Alcyonide and other compound cor- 
tical Polyps, muscles of any kind are equally 
invisible, and the contractions observable either 
in the substance of the common body or in the 
numerous hydriform mouths that minister to 
the support of the general mass, seem to be 
entirely due to the approximation of molecules 
diffused through the entire substance of the 
animal, rather than dependent upon any thing 
ike muscular structure ; nevertheless it has been 
Stated, though erhaps erroneously, that some 
families (the Pennatulide) are able to swim 
from place to place by consentaneous move- 
“ments of the polyps and polyp-bearing arms 
with which many species are provided. 
The tubular Polyps are equally devoid of 
so thing like muscular fibre, nevertheless the 
\ and uncalcified membrane that connects 
the Polyps to the cells wherein they are lodged, 
_ and the Hydriform Polyps themselves, are en- 
“dowed with the capability of performing all the 
_ Movements required to protrude the flower-like 
bodies from the cups that contain them, and to 
te and swallow the materials required for 
ir support. 
____ But in every group of animals, as we ap- 
= ope the most highly organized members of 
~ ‘that group, we find the characters of a more 
~ exalted type of organization beginning to ma- 
 -nifest themselves, and thus in the Actiniade, 
_ which are obviously osculent between the 
_ Aecrite Polyps and animals possessing a true 
_ Muscular system, a fibrous arrangement of the 
_ €ontracting portions of the body becomes very 
“distinctly recognisable, and a nervous filament 
‘May be displayed under favourable circum- 
_Stances passing round the oral extremity of the 
creature, and thus closely approximating the 
- hematoneurose type of structure. The infuso- 
rial animalcules ( Polygastrica, Ehren.) seem, as 
far as relates to their muscular system at least, 
to be strictly acrite animals, but such is their 
extreme minuteness, that much uncertainty 
MUSCULAR SYSTEM. 
In the Polypiphera we find a very extensive 
533 
still necessarily exists concerning their intimate 
organization. Their locomotive apparatus most 
frequently consists of fringes of vibratile cilia 
variously disposed, the movements of which 
are most probably dependent upon the exist- 
ence of a peculiar vital tissue distinct from 
muscle. In many species, e.g. the Proteus 
(Ameba diffluens), the contractions of the 
body are extensive, so that even the outward 
form of the animalcule is perpetually changing, 
and some, the Vorticelle, are attached to highly 
irritable pedicles of exquisite tenuity, that 
may be straightened or suddenly thrown into 
close spiral coils by some inherent power, the 
nature of which is as yet quite incompre- 
hensible. In some, as for instance Chilodon 
urcinatus, moveable hooks are found to be ap- 
pended to the surface of the animalcule, and 
some ( Nassula) are provided with a peculiar 
dental apparatus, consisting of a minute cylin- 
der of horny filaments; nevertheless no appear- 
ance of muscular or nervous fibre has as yet 
been detected even in the largest and most 
conspicuous species. 
The AcaLepn# next claim our notice as 
members of the Acrite division of the animal 
creation, and in every point of their economy 
they strictly conform to the general characters 
belonging to this type of organization. (See 
Acrira.) Their bodies are soft, pe'lucid, and 
gelatinous, without any trace of muscular fibre 
being perceptible in their composition ; their 
digestive canals are excavated in the paren- 
chyma of the body, not contained in any abde- 
minal cavity, and the canals through which 
nutrimentis conveyed to different parts of thesys- 
tem are entirely devoid of proper external coats ; 
neither, as'we believe, do nerves exist in any 
of the class, although, as we are well aware, 
two eminent observers have entertained a con- 
trary opinion. Professor Grant,* in his account 
of the anatomy of Cydippe pileus, describes a 
double ring of nervous fibre as surrounding 
one end of the alimentary canal of that beau- 
tiful little Acaleph, and has even figured ganglia 
distributed at intervals upon these circular 
cords, from which secondary nerves are de- 
scribed as emanating. Such a circumstance as 
the existence of nerves and ganglia in an ani- 
mal confessedly acrite, and presenting no traces 
of that type of structure which, in all other 
cases, invariably accompanies so elevated a 
condition of the nervous system, from its very 
singularity was well calculated to attract the 
notice of the physiologist, and we are ourselves 
quite satisfied that the distinguished professor 
has been led into error upon this point, most 
probably from having mistaken the circular 
canals, described by Delle Chiaje and others, 
as surrounding the ora! extremity of the Beroes, 
and which are indeed frequently filled with an 
opaline fluid, for nervous fibre.t 
* Vide Transact. of the Zoological Society of 
London, vol. i. and the figure at p. 109, vol. i. of 
this work. 
+ At the Birmingham meeting of the British 
Association, during a very interesting discussion 
npon this point, it was agreed by Mr. Forbes and 
Mr. Thompson, whose qualifications for such re~ 
