530 ME. H. M. BERNAED ON THE 



Apart, then, from any special theory as to the origin of the Arachnida, the evidence tends to show that 

 the primitive form had appendages which were leg-like, and serial with those of the cephalothorax, on 

 every segment of the abdomen. 



IV. The Cuticle and its Derivatives, and the Htpodermis. 



The Chitinous Cuticle. — The cuticle of Galeodes is very highly developed, and shows 

 many variations in adaptation to the needs of the different regions of the body. As a 

 rule, it is very thick and rigid in the anterior regions of the body, but soft and flexible on 

 the abdomen, with distinct but not very thick terga and " sterna." 



In this last point Galeodes comes halfway between the Spiders (with no terga * or sterna) and the 

 Scorpions, Pedipalpi, and Pseudoscorpions, which have well-developed sclerites on the abdomen, con- 

 tinuing dorsally the cephalothracic shield and ventrally the vestiges of sternites persisting between the 

 ■coxae of the limbs. 



The cuticle has the characteristic structure of the chitinous cuticle as found among 

 Arachnids, but it presents pecuJiarities which are of interest. Taking first a thick solid 

 portion (PI. XXIX. figs. 15 and 17), we have an outermost highly refractive pale yellow or 

 glassy layer (g), the colour of which deepens to bright red-brown when especially thickened, 

 as at the hinges, around the bases of hairs and spines, in the spines, in the jaws and 

 their teeth, &c. No structure can be made oiit in the outermost part of this layer ; its 

 inner part, however, can be seen to be finely striated, as if perforated by innumerable 

 fine canals which taper away into it. "Wlien, as in especially hard parts of the cuticle, this 

 layer is very thick, these canals show as a tangled mass of lines (fig. 17). This hard 

 refractive layer forms a continuous covering over the whole body, supplying the outer 

 coating of all the spines and hairs, and the innermost lining of the tracheae (PI. XXX. 

 figs. Via 8c lib). 



Pollowing this layer, and, as a rule, fairly distinct fi*om it, occurs a varying number 

 (often 30-40) of principal layers of whitish and comparatively soft chitin. They look as 

 if they gradually increased in hardness and refractiveness as they approach the outermost 

 layer, while the innermost layers often take slight stain. These are sometimes called the 

 chitinogenous layers. A high power seems to show that these principal layers are made 

 up of an enormous number of fine laminfe. They are traversed by innumerable canals 

 containing protoplasmic processes which sometimes stain deeply. Tliese canals seem to 

 end distally in the hard refractive outermost layer. The fine canals above described in 

 the glassy layer are in all probability the distal ends of the canals in the thick softer 

 layers. These " chitinogenous " layers can be followed into the hairs and spines, and 

 into the tracheae, where they form the solid hoops characteristic of these latter organs 

 (PI. XXX. fig.'j7 b). 



Both these layers ai'e modified in order to form the lens of the eye. The outermost 

 refractive layer appears to split up into a multitude of deeply staining layers, with 

 one (the outermost) extremely thin glassy membrane. The inner layers become 



* Except in LlpMsthis, cf. Pocock (59). 



