810 TUE 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. Frequentlj^, 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 tlic - ■/^^'i plane. In the calcareous shells, the 

 carbonate and phosphate of lii ru so intimately combined with the chi- 

 tinef, 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 c:l :", ihe^e 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 bordei'S of difierent parts of the cutane- 

 ous skeleton, are always mere prolongations or simple excrescences of the 

 inteo^ument, 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 

 oroans 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 inlays an important 

 part, for it probably secretes, in layers, the materials for the aew 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, Apux, Julus, and Glomeris. But 195, PI. XXI. fig. 9, a. b.) has observed with Cala- 

 in the last two of these, the cutaneous canals are nus arietis (an animalcule allied to Cyclnpsina 

 pretty lar{;e and consequently have not the appear- castor), two bristles at the extremity of each of the 

 aiice of black lines. long antennae, and which, he says, are provided 



3 According to f^alenl4n (loc. cit. p. 124), the with a row of vibratile cilia. But this observation 

 cutaneous canals of the Astacus ßuviatilis are does not invalidate what I have remarked in the 

 filled with carbonate of lime, a point which I have text, for how often have ciliary phenomena been 

 not had the opportunity to confirm. observed on organs which really have no such 



< Cyc.'ops, Cyclopsina, and other Entomos- appendages. I doubt if this observation of 7'em- 

 traca. pleton will be confirmed by other observers, 



fi Templet jti (Trans, of the Entomol. Soc. I. p. 



searches have convinced me of the vitality first, soft, sensible, and even furnished with vea- 



of the shell, at least in the first period of its exist- sels, but a quantity of calcareous mole soon collects 



ence ; and in reference to this, I am fully of there, hardens it, and obstructs the pores and ves- 



Cuvier's opinion, when he said, in his 'Anatomie sels ;'" see loc. cit. p. 376, also Comp. rend. 1847, 



Compar^e,' 'The envelope of the Crustacea is at XXIV. p. 12. — Ed. 



