310 THE CRUSTACEA. §.265. 
numerous very thin layers, made up of very fine, interlaced fibres. How- 
ever, sometimes this fibrous texture is scarcely distinguishable, and often 
the lamellae are perfectly homogeneous. Frequently, also, these lamellae 
are traversed, either in a parallel or perpendicular direction, by canals, 
which are often so small that, seen under the microscope by reflected light, 
they appear only as lines or black points. In some species, this skeleton 
has a distinct cell-structure ; for the skin, here and there, has the aspect of 
a net-work composed of numerous round, or polyhedral meshes. 
This net-work is, undoubtedly, the result of the fusion of the walls of 
numerous cells lying on the same plane. In the calcareous shells, the 
carbonate and phosphate of lime is so intimately combined with the chi- 
tine, that their particles, as such, cannot be distinguished. In those 
portions of the skin which serve a respiratory function, the calcareous 
matter is always wanting. . 
The pigments are due to very fine granules which exist either as such in 
the cutaneous lamellae, or are so thoroughly fused in these last, that they 
are indistinguishable. In some cases, these granules are contained in 
polyhedral cells which form a simple layer under the transparent skin; in 
others, radiating pigment cells, isolated, or reticulated, are seen through 
the colorless skin. The red, green, or blue color of many of the lower 
Crustacea, is due to oil-globules in the interior of the body, which are seen 
through the transparent integument. 
The tubercles, points, bristles, single or bifid hairs, which are usually 
hollow and exist on the surface or borders of different parts of the cutane- 
ous skeleton, are always mere prolongations or simple excrescences of the 
integument, and contain its characteristic substance, — Chitine. 
With Crustacea, as also with the other Arthropoda, the cutaneous 
envelope, whatever may be its tenuity —as for instance on the respiratory 
organs, is never covered with ciliated epithelium. This absence of vibratile 
organs is due, probably, to the presence of chitine. 
The internal surface of this envelope is usually lined with a peculiar, 
thin, fibrous membrane, analogous to an internal periosteum. In the 
moulting process, which is common to all Crustacea, it plays an important 
part, for it probably secretes, in layers, the materials for the new envelope. 
§ 265. 
Beside the cutaneous skeleton, there is, with the Cirripedia, an envelope, 
entirely resembling the mantle and the valves of the Acephala. 
2 Astacus, Apus, Julus, and Glomeris. But 
in the last two of these, the cutaneous canals are 
pretty large and consequently have not the appear- 
ance of black lines. 
3 According to Valentin (loc. cit. p. 124), the 
cutaneous canals of the Astacus fluviatilis are 
filled with carbonate of lime, a point which I have 
not had the opportunity to confirm. 
4 Cyc’ops, Cyclopsina, and other Entomos- 
traca, 
5 Templeton (Trans. of the Entomol. Soc. I. p. 
searches have convinced me of the vitality 
of the shell, at least in the first period of its exist- 
ence; and in reference to this, I am fully of 
Cuvier’s opinion, when he said, in his ‘ Anatomie 
Comparée,’ ‘The envelope of the Crustacea is at 
195, Pl. XXI. fig. 9, a. b.) has observed with Cala- 
nus arietis (an animalcule allied to Cyclopsi 
castor), two bristles at the extremity of each of the 
long antennae, and which, he says, are provided 
with a row of vibratile cilia. But this observation 
does not invalidate what I have remarked in the 
text, for how often have ciliary phenomena been 
observed on organs which really have no such 
appendages. I doubt if this observation of Tem- 
pleton will be confirmed by other observers, 
first, soft, sensible, and even furnished with ves- 
sels, but a quantity of calcareous mole soon collects 
there, hardens it, and obstructs the pores and yes- 
sels ;’’? see loc. cit. p. 376, also Comp. rend. 1847, 
XXIV. p. 12.— Ep. 
