REDFERN, ON FLUSTRELLA HISPIDA. 99 
spirit, in which they are remarkably distinct. The insertion 
of the great retractor into the lophophore, the pharynx, and 
cesophagus, is beautifully seen in the animal removed from 
its cell by dissection, as in fig. 4. 
The great retractor muscle consists of a long ecylindriform 
bundle of fibres, stretching from the deepest part of the cell 
over the stomach, to reach the cesophagus, pharynx, and 
lophophore, into which the fibres are inserted. Another 
bundle of much shorter fibres extends from the side of the 
cell, near its bottom, to the cul-de-sac of the stomach, into 
which it appears to be inserted, drawing this part of the 
organ downwards and towards one side when in action, and 
thus assisting i folding the parts of the alimentary canal 
upon each other, that they may be easily accommodated in the 
interior of the cell. Yet neither these fibres nor any of 
those of the great retractor muscle remain attached to 
the stomach of the polypide withdrawn from its cell. I 
have examined the perfect stomach thus removed in at 
least twenty instances, and in none have I seen a single 
fibre attached to the wall of the stomach, whilst, in every 
case, the torn pharyngeal fibres remain connected with 
it. Four or five distinct bundles of muscular fibre stretch 
from the interior of the cell, at different points, to the 
polypide; passing transversely to the axis of the cell. 
Other bundles of at least two different muscles extend from 
the upper part of the interior of the cell to the mvaginated 
portion, which forms the sheath of the tentacles during the 
retraction of the polypide. The longer of these bundles is so 
much relaxed durig complete retraction, that it is bent upon 
itself. 
During retraction, the csophageal end of the stomach is 
rapidly drawn down to the bottom of the cell on one side, 
the cul-de-sac of the organ to the bottom on the other side ; 
the pyloric end of the stomach is folded upon the upper cur- 
vature, the pyloric orifice being brought very close to the 
cesophageal; the intestine is bent upon the pyloric end 
until the two lie parallel; and the tentacles are folded in a 
somewhat spiral manner, close to the intestine which lies by 
their side. Thus the cesophageal and pyloric ends of the 
stomach, and the dilated commencement of the intestine, are 
folded and lie parallel to each other directly across the axis 
of the cell, in the state of retraction, whilst they lie with their 
axes parallel to that of the cell, in the state of protrusion of 
the polypide. The act of retraction is sudden and rapidly 
completed, like that of voluntary muscles in general; the 
act of protrusion is performed very slowly, as if the tenta- 
VOL. VI. I 
