THE SKIN AND ITS APPENDAGES. 



375 



webs. The sui:»plemental toe presents, in the male, a rounded, oval 

 swelling (Fig-. 234 I, I)), with the end of the digit projecting from 

 the distal end. 



Normally this swelling is usually of a 

 grey colour; during the breeding season, 

 however, the swelling enlarges, and be- 

 comes of a black or deep brown colour 

 (Leydig). 



The epidermis covering this swelling 

 (Fig. 233) is much thickened and produced 

 into projecting papillae. The cutis also 

 shows a marked thickening and an increase 

 in vascularity ; the glands are of the kind 

 described as mucous glands (Engelmann). 

 They present, however, an immense increase in size, and at the 

 same time are so closely applied to one another as to form 



Vertical section tli rough the 

 epidermis of the supple- 

 mental toe of Rana escu- 

 knta ; after E. Schultze. 

 JIagnified 400 times. 



Fig. 234. 



II. 



W W 



Fore-foot of a male frog. 

 D Glandular swelling on the supplemental 



toe. 

 JK Warty papillae on the iuter-pludangeal 



joints. 



Vertic;il section through the swelling on the supplemental toe 

 of a male frog. 



B Blood-vessels. 

 Co Cutis. 

 D Glands. 

 Ep Epidermis. 

 M Muscles. 

 P Pigment-cells. 



the main part of the enlargement (see also Organs of Tactile 

 Sensation). 



In the webs the various layers of the corium are more or less 



