PARACOUOTOCA AKERMANI (wAUREN). 



321 



Thus the chitinous plates or sclerites of tlie bod\' ai-e 

 hardened areas of the general cuticle. This hardening of 

 the cuticle may involve both the epistracum {epi.) and endo- 

 stracum {end.), as in the case of the head-capsule, and the two 

 layers may then become quite indistinguishable and con- 

 tinuous; or it may involve only the endostracum, as in the 

 case of the metasternite. Here the epistracum overlies 

 the hardened endostracum, and is separated from it by a 

 narrow space (text-fig. 3, mt. st.). 



To some extent the genei-al cuticle varies in thickness in 

 different parts of the body, and genei'ally the thicker the 

 cuticle the greater the vei'tical height of the hypodermal 



Text-fig. 3. 



Paracoi'otoca akermani. Longitudinal section through ventral 

 exoskeleton of one abdominal segment. 



epithelium. The cuticle has been examined carefully with 

 Zeiss Ap. 1"5 mm. and H. Imm., and it may be definitely 

 affirmed that there is no general system of minute canals per- 

 forating it. The endostracum stains to some extent with 

 haematoxylin, and this is also the case with the epistracum in 

 certain parts of the body. It is thought that the staining* 

 capacity of the cuticle is associated with a certain looseness 

 in texture which will permit the passage of gases and even 

 fluids, although no actual pores may be visible. The only 

 place where there appeared any definite signs of a canalicu- 

 lation of the exoskeleton was in the sternal region of the 

 metathorax in front of the acetabulum of the third pair of legs 

 (PI. XVII, fig. 35, end.). Here a distinct vertical or oblique 

 striation could be seen in the sections. This striation seemed 

 to be caused by the presence of very numerous minute cracks 

 or caiials which, however, did not appear to reach the 



