CONSIDERATIONS. 467 



articulations in different directions, it retains a sufficient degree 

 of flexibility. This constitutes the chief difference between 

 the teguments of vertebrate and articulated animals, although 

 the armadillos in the former offer a similar example of an 

 ossified skin. 



In the Annelida abranc/iia, especially in the genus Hirudo, 

 the skin presents the same structure as in the Vertehrata, 

 except that the papillary tissue is apparently wanting; the 

 mucous matter,^ which is very abundant and nearly fluid, is 

 placed immediately beneath the corneous and nearly colour- 

 less epidermis ; the dermis is a very thick membrane, of a 

 close texture, formed of fibres irregularly transverse to the 

 direction of the body ; it appears to consist of but one layer. 



In the genus Limulus the teguments consist of two lamina, 

 easily separable ; the first, corneous, brown, thick, analogous 

 to the epidermis ; the second, analogous to the dermis, still 

 thicker, of a pale yellowish colour, corneous, but of a less 

 compact structure than the first: beneath this is a copious 

 black mucous matter. 



In insects the teguments consist also of three layers, as in 

 the Annelida and Linmlus, but they present peculiar charac- 

 ters. The mucous, or more properly the colouring matter, is 

 composed of two separate substances ; the one soluble in 

 alcohol, forming in many insects, especially the Coleoptera, 

 the outer layer, giving those brilliant colours with which many 

 are adorned ; the other, not soluble in alcohol, generally of a 

 brown or blackish hue, is mostly contained in the tissue of the 

 dermis and epidermis. In Coleoptera the epidermis forms 

 the second layer of the teguments ; is thin, hard, brittle, 

 friable, and without any trace of fibres ; its colour is gene- 

 rally black or brown. The dermis consists of many distinct 

 layers, easily separable, composed of fibres more distinct in 

 proportion as the layers are more internal. The dermis is 

 paler than the ejjidermis, being brownish or white. 



The internal prolongations of the teguments appear to be 

 formed by the dermis, intermixed with a small quantity of 

 the colouring matter. 



The colouring matter is found sometimes between the 



' I use the term mucous matter, as employed by M. Straus, in preference to 

 rete mucosum, because I conceive the latter term hardly applicable to an almost 

 fluid substance as this is in insects. — D. 



