240 Description of a Species of Caligus. 
members, like those of animals having a soft skin, appear to in- — 
crease in actual quantity of matter, as rapidly when enveloped in 
their unyielding corneous covering, as in their new membranous 
envelop. 
There is aremarkable fleshy appendage to the anterior portion 
of the soft internal animal, the importance or functions of which 
we are unable to explain. It is represented at mn, fig. 23, in its 
natural position. It lies wholly external to the inner shell, and is 
attached only at 0, its anterior extremity. Figure 24 isa profile 
view of this appendage; similar letters mark the corresponding 
parts in the two figures. After separating the outer skin, it may 
be drawn forward into the position in fig. 25. In one instance, we 
found an animal with this singular appendage, in front, presenting 
very much the appearance in fig. 25. It was, however, composed 
of three of these appendages, mn, placed end to end, and ap- 
peared to have undergone three successive moultings. 
In external appearance, this organ very much resembles a mus- 
cle, as it is striated, like them, though very coarsely. It is proba- 
bly attached, by its large extremity, to the outer shell. 
If. Muscunar System. 
The muscles moving the several members, may, in general, be 
distinctly seen and traced to their insertions through the pellucid 
covering of the body. Yet, under a magnifying power of five 
hundred diameters, we have not succeeded in detecting the ulti- 
mate fibres as given by Straus. With a much lower power, how- 
ever, we have observed that all the muscles appear transversely 
striated, and by means of this important character, have been ena- 
bled to distinguish the nerves from the muscles, which, without 
this aid, would in many instances have been difficult or even im- 
possible. These striations are most distinctly seen in the flat, sim- 
ple muscles ; those composed of several bundles of fibres, which 
is the case with many of the large muscles on the back, exhibit 
it, but less perfectly. We have examined the muscles of the 
common lobster, (Astacus marinus,) and have found these striz 
in some instances, though with less distinctness. These stria- 
tions vary much in their fineness. In general, they are from 
a3 tO =,55 of an inch apart. In some muscles, among whic 
we may mention those elevating the buccal mass, we found them 
as as ;;'55 of an inch. We have conjectured that they are 
