486 



TEGUMENTATIY ORGANS. 



another at right angles, so that they form two 

 sets of opposite spirals. The fibres are sharply 

 contoured, dense, and brittle, and those of 

 each layer are divided into six sets, corre- 

 sponding with the six sections of the body. At 

 the sutures the fibres of each bend back upon 

 themselves, and run in a parallel course to the 

 opposite suture. 



The deep layer is the thickest ; it appears 

 longitudinally striated on section, and may 

 be split into lamellae of any thickness ; other- 

 wise it is perfectly structureless. 



In the Nemertidae, according to the re- 

 searches of Quatrefages, the integument has 

 essentially the same structure, consisting of a 

 superficial structureless ciliated lamina, with 

 deeper vacuolated and fibrillated layers. In 

 the other Turbellaria the vacuolated struc- 

 ture is predominant. 



This fibrous chitinous integument is still 

 better developed in the Insecta. 



According to Mayer (I. c.) the chitinous 

 integument of Lucanus cervus is composed of 

 glassy rods with sharply defined dark, paral- 

 lel edges, which by their mutual apposition and 

 anastomosis, and probably by the interposition 

 of a connecting mass, form thin layers. The 

 rods in each layer are parallel, but those of 

 different layers cross one another at angles of 

 from 45 to 90; so that a horizontal section 

 presents a sort of elegant cross-hatching, the 

 lines of which are about G'008 mm. apart. 

 The outer surface of this laminated mass is 

 invested by a transparent homogeneous sub- 

 stance containing pigment, and above this 

 by a layer of epidermic " cells " (O'OOS to 

 O'Ol mm. in diameter), with 'nuclei and nucleoli, 

 their edges being separated by an intermediate 

 substance. Internally, there is also a layer 

 of epidermic " cells " which are polygonal from 

 mutual pressure. They are without nuclei, but 

 possess a short spine, arising from the centre 

 of the cell, and ending by a sharp point. 

 Quekett (/. c.) describes a similar structure, 

 consisting of striated laminae, in the integu- 

 ment of Dynastes Hercules. 



The integument thus described closely re- 

 sembles that of the larger Crustacea (vide 

 infra), and I should have placed it with them, 

 except for the very distinct statement of Mr. 

 Newport with regard to the development of 

 the integument in Meloe. According to Mr. 

 Newport's researches, the integument of the 

 young Meloe is at first composed of polygonal 

 nucleated cells, the largest of which is about 

 ^^LO of an inch in diameter. As the animal 

 grows, the nuclei divide and subdivide by a 

 process of fission, and the integument becomes 

 composed of several layers. After awhile, 

 the deeper of these undergo a fibrous meta- 

 morphosis, and constitute a fibro-cellular 

 structure, which gives attachment internally 

 to the muscles, while the external layers 

 continue to grow, and to be reproduced as 

 distinct cells. 



If this were the mode of development 

 which obtained in all Insecta we must con- 

 sider their chitinous integument to be pro- 

 duced by conversion of the previously ex- 



isting cells of the ecderon. However, Leydig's 

 statements are equally decided, that the in- 

 tegument of Corethra presents no appearance 

 of cellular origin, and the question may, there- 

 fore, for the present, probably be considered 

 undecided. 



The calcified integument of the Crustacea 

 presents the same general structure as that of 

 the other Annulosa, consisting of superposed 

 chitinous, more or less fibrous lamellae, the 

 outer of which are infiltrated with a calcareous 

 deposit. In the small transparent Crustacea, 

 as we have already seen, the integument is 

 composed of structureless layers, developed 

 by excretion on the surface of the ecderon, 

 and even in the largest forms, the minute 

 hairs, &c., present precisely the same ap- 

 pearance ; but in the thick integument of the 

 Decapoda, certain layers of the shell have been 

 described, not without considerable show of 

 reason, as possessing a cellular organisation 

 (Carpenter). 



I have carefully examined the shell of the 

 common crab in relation to this point, and the 

 following are the results of my investigation. 



It appeared to me in the first place, that, 

 without seeking for a moulting crab, the 

 structure of the integument in its uncalcified 

 state might be readily ascertained by ex- 

 amining the soft membrane connecting the 

 articulations of the limbs, which, as is well 

 known, is continuous on either hand with 

 the calcareous integument, and passes into it. 

 In a section of this soft Ia3 r er (fig. 312. A), I 

 found from within, outward, 1. The enderon 

 (a) composed of connective tissue, excavated 

 by vascular channels, and containing nume- 

 rous aggregations of pink and yellow pigment, 

 frequently disposed in a stellate form, or even 

 forming anastomosing net-works along the ru- 

 dimentary elastic fibres of the tissue. 2. The 

 surface of this (b) was constituted by a proto- 

 morphic layer, consisting of a homogeneous 

 substance containing endoplasts (c), which 

 sometimes adhered to the enderon, sometimes 

 to the hard integument, when the latter was 

 detached. 3. Superficial to this, was the 

 chitinous layer of the integument (c) com- 

 posed of a number of lamina; of great deli- 

 cacy, and not more than ^o 1 ^ f an nncn 

 apart. The deep laminae were much softer 

 than the superficial, and the outermost lamina 

 of all was hardest, and of a brownish colour, 

 constituting the structureless epidermis of 

 Carpenter and Lavalle. 



In section, the deep laminae (B) presented 

 only an indication of perpendicular fibrillation; 

 but this became more marked superficial!}', 

 the outer part of the section appearing closely- 

 striated. The deep laminae, when stripped off', 

 presented no definite structure, but they readily 

 fell into plaits ; while the superficial laminae ap- 

 peared dotted over. I sought in vain for any 

 appearance of endoplasts in the deep layer, 

 where, however, had they existed, they must 

 have been readily detected ; and I therefore 

 conclude, that the chitinous lamellae are formed 

 from the subjacent ecderon, by a process of ex- 

 cretion. It should be remarked, however, that 



