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 a remarkable 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 m n, fig. 23, in its 

 natural position. It lies wholly external to the inner shell, and is 

 attached only at o, its anterior extremity. Figure 24 is a 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, m n, 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. 



II. Muscular 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 striae 

 in some instances, though with less distinctness. These stria- 

 tions vary much in their fineness. In general, they are from 

 _^i__ to a oV of ^1^ inch, apart. In some muscles, among which 

 we may mention those elevating the buccal mass, we found them 

 as coarse as j Vo o ^^ ^^ inch. We have conjectured that they are 



