332 ■ ME. H. M. BEENAED ON THE 



varying thickness as its outer layer, beneath which follow several layers of hard, red-brown, highly 

 refractive chitiu (PI. XXX. fig. 1 h). These, again, are followed immediately by a varying but generally 

 considerable thickness of staining chitin, between the laminae of which pigment is found deposited. 

 The staining layers are found to be traversed by fine canals. This cuticle, like that of Galeodes, cuts 

 much more easily than does that of Lycosa ; though it is much thicker, it is much less brittle. 



Where the cuticle is thin and flexible, as on the abdomen, we naturally find a striking 

 change in the arrangement of the layers. The outermost hard refractive layer is thrown 

 into minute transversely arranged folds (PI. XXX. fig. 6) in all parts wherever the skin is 

 required to bend, i. e. at the sides of the body and between the consecutive tergites and 

 " sternites." Over these latter it lies flat. 



Immediately under this folded refractive layer, a great number of very thin staining 

 layers occur which appear to be thrown into irregular wavy folds, and do not in any way 

 repeat the regular folding of the refractive layer as seen iu section. Pigment masses are 

 occasionally found deposited between these staining layers. I have not discovered the 

 origin of these pigment masses ; as a rule, the pigment of the dorsal surface is seen 

 within the hyj)odermis-cells. 



This folding of the outermost layer seems to be universal over the abdomen of the Spiders, which 

 Lave generally lost the smooth, non-flexible tergites and sternites. The curious ridging of the flexible 

 cuticle in the Spiders has been much discussed, and the ridges have been thought to be thicknesses of 

 skin rather than folds [Wagner, 74). It seems, to judge by Galeodes, that both statements are true; 

 the skin itself is not folded but simply regularly thickened by foldings of its outermost refractive layer, 

 these folds not being repeated by the subjacent layers (PI. XXX. fig. 3). 



These subjacent staining layers pi-esent a I'emarkable feature. The usual lamination parallel to the 

 surface of the skin is obliterated for a certain depth under the outermost refractive layer by an immense 

 number of fine canals which open through pores in the outermost layer. The apertures of these pores 

 appear to lie in the troughs formed by the ridges ; the surface view of these pores has already been 

 figured and described by Wagner. Tliis marked porosity of the cuticle in the abdomen of the Araneids, 

 which may be a specialization of the canal system described in the cuticle of Galeodes, may perhaps be 

 brought into relation with the loss of the excretory functions of the Malpighian vessels, which appear 

 to have become specialized for the removal of the faeces from the mid-gut diverticula (n). It is also 

 probably a protective adaptation to render distasteful their otherwise attractive sac-like abdomens filled 

 to distension with rich food. 



Beneath this porous layer there are to be found a few layers of staining chitin, probably permeated by 

 the hypodermis cells. 



These remarkable lines and ridges on the cuticle of the whole abdomen of Spiders are found also on 

 all soft-bodied Mites. This is perhaps a further point of connection between the Acari and the 

 Araneai, such striation occurring, so far as I know, in no other Arachnids (6). 



So far as I can ascertain, it is the outermost refractive layer of chitin which, by being thrown into 

 ridges and folds and conical processes, cause the remarkable sculpturing of the cuticle of the Phalangida, 

 the lower layers taking no definite part in it. 



Scorpio [Eiiscorpio) has no ridged and furrowed cuticle, such as Galeodes, Spiders, and Acarids. 

 The flexible membranes at the sides of the body between the terga and sterna are thrown into irregular 

 folds covered by the glassy layer arranged as shown in PI. XXX. fig. 2. This white and highly refractive 

 outermost layer shows no lamination, but is apparently traversed, at least for some distance, by canals. 

 The inner chitinogenous layers stain deeply, but take no part in the formation of the papilla- like folds {?) 

 of the glassy layer. 



