598 DR. W. C. M'INTOSH ON THE HAIRS OF CARCINUS MANAS. 
under the old shell on the surface of the new. It is quite separate from the other 
layers of the old shell, and soon disappears from the new after the moulting. Micro- 
scopically it presents numerous phosphatic crystals and calcareous masses, which 
evidently are extraneous to its structure, since, when well washed, it is only granular, 
and the apertures of tubuli are not distinct. Beneath this, the hairs are found every- 
where in their peculiar sites ; but there is nothing to warrant the supposition of Réaumur 
that they are pulled from the sheaths of the old textures. Not to speak of the impossi- 
bility of this as regards the minute anatomy of the Crustacean shell, the hairs are found 
lying flatly on the new shell beneath the old, while the hairs of the latter have the same 
situations and identically the same structure as formerly ; but they are often loaded with 
parasites, both vegetable and animal. Milne-Edwards, on the other hand, states that no 
hairs are found (in such species as possess them) when the old shell still adheres to the 
back of the animal,—a view which the above observation negatives in this species. The 
new hairs are very pale and translucent, the central faintly defined from the outer por- 
tion. The surface of the cuticle about the bases of many of these hairs was studded with 
an immense number of the minute cuticular spikes formerly described, and which seem 
to follow a certain order in their occurrence, being absent from some portions of the 
cuticle. 
The process of exuviation not only furthers various ends in the growth of the animal, 
but it also fulfils an important function in regard to the parasitic structures on the 
hairs; for if the parasites continued to flourish on a Crab which did not periodically 
undergo this change, its condition can scarcely be imagined. Moreover, since it has 
almost been proved that the hairs are organs of sensation to the animal, it can readily 
be conceived that their functions in this respect would be greatly interfered with, if not 
in some cases destroyed, did not the exuviation at once clear the cuticle and its append- 
ages and thus further the well-being of the Crab. 
