YOUNG MUCOUS GLAND SPENT MUCOUS GLAND 



MIXED GLAND 



Figure 8-14. Sections through various epidermal glands of Necturus. A, young mucous gland; B, 

 spent mucous gland; C, poison gland; D, mixed mucous and poison gland. 



glandular and function along with the saccular mucous 

 glands. In the salamander, the poison glands are nearly the 

 same size as the mucous glands, but the lining of secretory 

 cells is of a more irregular thickness and has clumps of 

 nuclei. The granular contents of the gland is somewhat dif- 

 ferent in appearance from that of the mucous gland. The 

 epidermis of Cryptobranchus is invaded by blood capillaries as 

 a part of the respiratory fiinction of the skin. 



The skin of the Gymnophiona is thick and contains groups 

 of dermal scales and large multicellular posion glands of a 

 holocrine (entire cell breaks down) type (Figure 8-15). 



The epidermis of the early embryo is composed of an 

 outer ciliated periderm and a deeper stratum germinativum. 

 This condition persists up to a size of about 10 mm. when 



the epidermis, now somewhat thicker, loses the cilia and be- 

 comes covered by a thin hyaline (clear) cuticula of secreted 

 material similar to the basement membrane and the inter- 

 cellular substance. 



Choanate fishes 



The skin of Latimeria is described as simple in structure. 

 The epidermis is stratified and has a thick basement mem- 

 brane. There are mucous cells and chromatocytes in the 

 epidermis. The dermis is thick, fibrous and has many fat 

 cells. 



In Protoplerus, a dipnoan, the epidermis is stratified with 

 a basal, low columnar stratum germinativum and four or 



head 



calcified squomuia^ 



ayers of fibers 



basal pseudoepithelium 

 outer columellar fibers 



basal fibrous layer (stratum compactum}' 



A 



B 



Figure 8-15. A, section through the skin of /chfhyophis g/uh'nosus showing glands and groups of 

 scales enclosed in sacs. B, enlarged section of a scale showing the various layers. (After P. and F. 

 Sorosin, 1887) 



224 . THE SKIN AND ITS DERIVATIVES 



