310 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 houiogerieoup. Frequently, also, these lamellae 

 are traversed, either in a parallel or perpendicular direction, by canals, 

 virhich 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, thei^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 ai-e usually 

 hollow and exist on the surface or borders of difi"erent parts of the cutane- 

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

 intectument, 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 Jrstacus, Apus, Julus, and Glomeris. But 195, PI. XXI. fig. 9, a. b.) has observed with Cala- 



iri the last two of tliese, the cutaneous canals are mis arintis (an animalcule allied to Cyclopsina 



pretty lavj;e and consequently have not the appear- castor), two bristles at the e.xtremity of each of the 



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



■i According tf> Falentin (loc. cit. p. 124), the with a row of vibratile cilia. But this observation 



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



tUl'jd with carbonate of lime, a point which 1 have te.xt, for how often have ciliary phenomena been 



not had the op])ortunity to confirm. observed on organs which really have no such 



■4 Cyclops, Cyclopsina, and other Entomos- ajjpendages. 1 doubt if this observation of Tem- 



traca. pleton will be confirmed by other observers. / 



5 Templeton (Trans, of the Entomol. Soc. I. p. 



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



of the shell, at least in the first period of its exist- sols, 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 ve»- 



Cuvier's opinion, when he said, in his 'Anatomic sels ; '" see loc. cit. p. 376, also Comp. rend. 18-i7, 



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



