35 THE BIOLOGY OF THE FROG chap. 



cavity. The oviduct is also enlarged before and during the 

 breeding season. The glands in its wall reach a high degree 

 of development and secrete an enormous amount of a mucus- 

 like substance around the eggs as they pass down the lumen. 

 After the eggs are discharged, the glands diminish in size and 

 activity, and the size of the whole duct is much reduced. 

 There is a diminution in the size of the testes after the 

 escape of the spermatozoa and then a gradual increase in 

 size during the summer until fall. 



Correlated with the ripening of the spermatozoa and the 

 appearance of sexual instincts of the male frog there is an 

 increased development of the base of the inner digit of the 

 fore arm and an enlargement of certain muscles which are 

 concerned in the clasping reflex. Both the inner digit and 

 clasping muscles are larger in the breeding period than at 

 other times, and it is probable that their increased develop- 

 ment is dependent upon changes taking place in the sexual 

 glands. Sometimes there are certain external characters 

 developed in the female also during the breeding season. In 

 the females of Rana tcmporaria Huber has described der- 

 mal papillae which occur especially upon the back and sides 

 of the body and the upper surface of the legs. On the back 

 they are usually confined to the posterior half of the body, 

 but on the sides they extend forward nearly to the tip of the 

 nose. In the male the skin is entirely smooth or possesses 

 in a few cases only very small papillae. The color of these 

 papillae is a whitish or light rose, and they are rounded 

 or cone-shaped in outline, and four to five millimeters in 

 diameter. They are richly supplied with blood, but are 

 entirely devoid of dark pigment. When sectioned they 

 are shown to be due mainly to a thickening of the outer 

 portion of the cutis and to be made up largely of con- 

 nective tissue. The overlying epidermis is not noticeably 



