82 THE MICROSCOPICAL NEWS, 
called the pyloric vestibule. Here the food is formed into pellets 
prior to ejection. The pyloric vestibule is richly ciliated. 
In some species of polyzoa, between the cesophagus and the 
stomach is found a gizzard, which is an enlargement of the cardiac 
portion. The walls are much thickened, very muscular, and pro- 
vided with pointed processes called gastric teeth. 
III. The nervous system is present in a very rudimentary form. 
It consists of a single roundish ganglion, from which nerves are 
given off in different directions. ‘These nerves are very difficult to 
follow. They have been traced to the lophophore, the tentacles, 
and the alimentary canal. 
IV. As may well be imagined, the muscular system of the 
polyzoa is complex and highly developed. The varied movements 
of the corona as a whole, and of the separate tentacles, of the 
alimentary system, of the endocyst, &c., shew that to effect them 
there must be present a full apparatus of muscles, and we find this 
to be the case. The principal muscles are the great retractors. 
These consist of two broad bundles of fibres attached to the lower 
part of the cell wall and extending to the base of the tentacles. In 
the expanded polypide they appear as two bands extending the 
whole length of the organism, when contracting they drag down the 
corona, invert the sheath, double up the alimentary canal, and 
bring all parts well within the cell very rapidly. 
These muscular bands, though really solid, are made up of a 
number of fibres which separate on relaxation. The muscles of all 
polyzoa are simply distinct fibres which never unite in the man- 
ner observed in the higher animals. ‘The fibre appears striated in 
some of the larger muscles. 
The interior of the animal, z.e., the space between the endocyst, 
in which the alimentary canal is suspended, is called the perigastric 
cavity, which is always filled with fluid in which float a large num- 
ber of corpuscles of various shape and size, and into which are 
discharged the spermatozoa. Within this cavity the reproductive 
organs are lodged, and here the ova passes through their stages 
into the larval forms. 
This fluid has been analysed in one or two cases and found to 
be a concentrated solution of common salt, with traces of albumen. 
It may be assumed to consist in all cases of water and the pro- 
ducts of digestion, though how these get into the cavity is not 
known. The only hypothesis is that they traverse through the 
walls of the alimentary canal. 
The particles are the cells of the endosarc, and have been 
compared to the blood corpuscles of the lower animals. 
The perigastric fluid extends into the tentacles, where, as in a 
system of gills, it is aerated by the water. 
At the lower part of the cell, and connecting the base of the 
