402 EXTERNAL ANATOMY OF INSECTS. 



colours of the skin are mixed in its horny tissue, nearly as 

 those of the Testacea are in their calcareous shells a . In 

 the perfect insects, therefore, in most cases, we may con- 

 sider the epidermis and rete mucosum as together form- 

 ing the exterior and coloured integument of insects — 

 that part which in the table, since it is not properly an 

 epidermis, I have distinguished by the name of Exo- 

 derma. 



The learned author just quoted has observed nothing 

 under the skin of white-blooded animals that he regards as 

 analogous to nervous papillae b . In some parts of insects, 

 as in the lamella? of the antennae of the Petalocera, and the 

 extremities of the joints, especially the last, of many palpi, 

 there is however an appearance of them ; and it seems 

 reasonable to suppose that where the sense of touch re- 

 sides, there must, even in insects, be something of a pa- 

 pillary tissue. 



With regard to the innermost integument of the ver- 

 tebrate animals, — the leather, or real skin, — this learned 

 comparative anatomist finds nothing analogous to it in 

 the integuments of insects c ; but as he does not notice it, 

 he appears to have overlooked the substance that lines 

 the outer crust, or exoderma, in the Coleoptera and most 

 other orders. This is not always easily detected ; but it 

 may generally be discovered by breaking, or rather tear- 

 ing (not cutting), after having cleared away the muscles, 

 any part of the body of an insect. It is always very vi- 

 sible on the under side of elytra d , but is not discoverable 



a Anat. Compar. ii. 553. b Ibid. 557. c Ibid. 560. 



4 Plate XXVIII. Fig. 2. a"'. 



