SECT. II 



THE OUTER BODY FORM 



23 



on exposed angles, edges, or surfaces, as, for instance, 

 round the posterior segments (see frontispiece). 



(4) There are thickenings for the formation of 

 rudimentary articulations, especially of the limbs upon 

 the body and of the joints of the limbs on each other. 

 Figs. 4 and 5 give two views of one and the same leg 

 of a large specimen of Apus cancriformis. In these 



^7^2 



Ficj c —Posterior (convex) aspect of the same leg, the skin being nearly all thin and 

 'senil-transparent, but showing rudimentary hinges A few muscles are indi- 

 cated. Lettering the same as in Fig. 6. On the endites are seen the denticulate 

 setae referred to on p. 46. 



the thickenings forming rudimentary hinges are very 

 instructive, the rest of the cuticle of the leg, with 

 the exception of the thickened strips and areas for 

 the counteraction and attachment of muscles, being 

 thin and flexible. It would be an interesting mechanical 

 problem to try to discover why the bent concave side 



