J ON FRESHWATER POLYZOA. 319 
examined, the fracture will be found to have occurred in a plane perpendi- 
cular to the axis of the fibre, never presenting an uneven or lacerated ap- 
pearance; and a marked tendency to separate into discs may be recognised 
in the detached and broken fibre. When the fibre is in an uncontracted 
state, it would seem to be perfectly cylindrical, and the normal act of con- 
traction is so momentary that its condition during this act cannot be wit- 
nessed. When, however, the living polypide is torn from its cell, the rup- 
tured fibres which continue attached to its body are thrown into a state of 
spasmodic contraction, and then it will be seen that they lose their cylindri- 
city and become irregularly swollen at intervals, while the whole fibre has 
much increased in thickness: in this state we may also observe it obscurely 
striated. The swellings here visible in the contracted fibre are quite differ- 
ent from the peculiar knots described by Dr. A. Farre in the muscles of 
the marine Polyzoa. Such knots do not exist in the freshwater species, at 
least 1 have never seen them, with the exception perhaps of certain little 
swellings, which may be occasionally witnessed in the parietal muscles of 
Paludicella and in the superior parieto-vaginal muscles of Plumatella. In Pa- 
ludicella 1 have witnessed a curious phenomenon presented by the muscular 
fibre. In this polyzoon the fibres of the great retractor muscle, while lying 
relaxed in the bottom of the cell after the retraction of the polypide, may 
frequently be seen to present a singular motion, impressing you with the 
idea of a cluster of writhing worms. 
The existence of striated fibre in the Polyzoa was first noticed by Dr. 
M. Edwards, who detected it in Bschara*; and Mr. George Busk has since 
described and figured the same form of tissue in Anguinaria spatulata and 
Notamia bursariat. 
E. Organs of the Life of Relation—I have succeeded in making out a 
distinct nervous system in all the genera with the exception of Paludicella, 
in which I have not as yet been able to effect any satisfactory demonstration 
of its existence. Jn all the species with bilateral lophophores, there may be 
seen attached to the external surface of the c:sophagus, on its rectal aspect 
just below the mouth, an oval body of a yellowish colour. Careful examina- 
tion shows that this body is furnished with a cavity or ventricle in its inte- 
rior ; that it is a nervous subcesophagean ganglion there cannot be any doubt, 
and I have succeeded in distinctly tracing nervous filaments’in connection 
with it. In Cristatella, Lophopus, and other genera with crescentic lopho- 
phores, the ganglion may be seen giving off from each side a rather thick 
chord, which takes a course backwards, and immediately enters the tubular 
arms of the lophophore, and then running along the roof of this cavity, gives 
off at regular intervals a filament to each tentacle upon the outer margin of 
the arm. When it arrives at the extremity of the arm it turns on itself, and 
in its retrograde course gives off similar filaments to the tentacula placed 
upon the inner margin. I have thus traced it back to the base of the arms, but 
have here failed in my attempts to follow it further; it is however highly proba- 
ble that it passes across the lophophoreto unite with the corresponding filament. 
of the opposite side. The ganglion also sends off filaments upwards towards 
the mouth; and a filament may be observed passing downwards along the 
᾿ esophagus, and soon losing itself on the walls of this tube. I have made out 
this last filament very distinctly in Cristatella. From each side a delicate 
filament would seem to pass forwards on the cesophagus, but I have not sue- 
. * Milne-Edwards, Recherches Anatomiques, Physiologiques et Zoologiques sur les Eschares, 
_ Ann. des Sci. Nat., 2de Serie, t. vi. 
+ Busk in Transactions of the Microscopical Society of London, vol. ii. 
