390 TEGUMENTARY ORGANS 



small plates could be detected, making up the large ones. Dr. 

 Meissner calls them " cells," but expressly states that he never 

 detected any nucleus in them, and it seems more probable that they 

 are produced by modifications of the original external structureless 

 layer, similar to those which, as will be seen, occur in the Crustacea 

 and Mollusca. 



The middle substance of this integument is composed of two 

 layers of fibres one above the other. The fibres are parallel in the 

 same layer, but those of the two layers cross one 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, corresponding 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 lamellje of any thickness ; otherwise 

 it is perfectly structureless. 



In the Nemertidae, according to the researches of Quatrefages, the 

 integument has essentially the same structure, consisting of a super- 

 ficial structureless ciliated lamina, with deeper vacuolated and 

 fibrillated layers. In the other Turbellaria the vacuolated structure 

 is predominant. 



This fibrous chitinous integument is still better developed in the 

 Insecta. 



According to Mayer (/. c.) the chitinous integument of Lucanus 

 cervus is composed of glassy rods with sharply defined dark, parallel 

 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 

 O'OoS mm, apart. The outer surface of this laminated mass is 

 invested by a transparent homogeneous substance containing pig- 

 ment, and above this by a layer of epidermic "cells" (o'OOS to O'Oi 

 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 laminse, in the 

 integument of Dynastes Hercules. 



The integument thus described closely resembles that of the 



