INTEGUMENT 



19 



layer is composed of more cylindrical or cubical cells. The former 

 corresponds to the stratum corneum, the latter to the stratum 

 Malpighii. The horny layer is shed periodically, either entire or 

 in pieces. 



Later, with advancing development, the layers of the epidermis 

 become more numerous, and involutions towards the dermis take 

 place in all parts, giving rise to a great number of sac-like and 

 tube-shaped glands similar to those of Protopterus (p. 17) ; these 

 are particularly abundant in certain regions— more especially on 

 the head and flanks (Fig. 12). The individual glands are sur- 



'^Tm 



Fig. 12. — Section through the Skix of Adult Sala:maxder (S. maculosa 



Ep, epidermis ; Go, dermis, in the richly pigmented (Pi) connective-tissue stroma 

 of which tlie various sized integumentary glands (A, O, D, D, E) lie embedded ; 

 3P, the muscular layer of the glands, lying within the basement membrane 

 (Pr) ; M, the same, seen from the surface ; E, epithelium of glands ; .S', 

 secretion of glands ; Mm, subcutaneous layer of muscles, through which 

 vessels ((?) extend towards the dermis. 



rounded by muscle and connective-tissue fibres, pigment, blood- 

 vessels, and nerves. Their secretion serves to keep the skin moist, 

 but as experiments have shown, it also forms an important weapon 

 of defence on account of its poisonous properties. 



This richness in glands is a characteristic of the skin of Amphi- 

 bia and to it they owe their moist and slippery nature. Frequently, 

 as for instance in Toads, the skin is not smooth, but has a rough, 

 warty appearance, caused by local proliferations of the epidermis. 



Epidermic claws, analogous to those of the Amniota, are present 

 only in Xenopus (Dactylethra) and Onychodactylus. 



The pigment, accumulated principally in the dermis — partly 

 diffused, partly enclosed within the cells — is under the control of the 

 nervous system, and thus renders a change of colour possible ; and 



