24 



INTRODUCTION. 



a stripped skin held against the light, gives rise to the 

 yellow vertebral line which is normal in. Bm/o calamita, 

 and only exceptional in B. vliiJls and wiiZ^ar/s, inde- 

 pendently of another light vertebral streak which is 

 sometimes also present. The independence of the 

 two is most conspicuous in cases of deviation of the 

 former, as often happens in Bafo calamita, which 

 appears to be caused by the presence of large glands 

 in the course of the raphe necessitating a winding 

 (Fig. 9). 



Fig. 9. 



Biifo calamita, showing yellow raphe, independent of light 

 vertebral streak, and its deviation from the median line in 

 the middle of the back. 



The epidermis is remarkable for the formation of 

 horny cells, as the spines on the warts of some toads 

 and Bomhlnator (Fig. 10, p. 29), or the sheaths on 

 the tips of the digits in Bnfo and Pelobates, or on the 

 metatarsal tubercles Avhen these are much developed. 

 There are also, in some Batrachians, special small, 

 pearl-like warts, mostly pigmentless, the "tact-spots" 



