454 THE DESCENT OF MAN 



toad which I ever saw, the Phryniscus nigricans " had the 

 whole upper surface of the body as black as ink, with 

 the soles of the feet and parts of the abdomen spotted 

 with the brightest vermilion. It crawled about the bare 

 sandy or open grassy plains of La Plata under a scorching 

 sun, and could not fail to catch the eye of _ every passing 

 creature. These colors are probably beneficial by making 

 this animal known to all birds of prey as a nauseous 

 mouthful. 



In Nicaragua there is a little frog "dressed in a bright 

 livery of red and blue" which does not conceal itself like 

 most other species, but hops about during the daytime, and 

 Mr. Belt says" that as soon as he saw its happy sense of 

 security, he felt sure that it was uneatable. After several 

 trials he succeeded in tempting a young duck to snatch up 

 a young one, but it was instantly rejected; and the duck 

 "went about Jerking its head, as if trying to throw off some 

 unpleasant taste." 



With respect to sexual differences of color, Dr. Grunther 

 does not know of- any striking instance either with frogs 

 or toads; yet he can often distinguish the male from the 

 female by the tints of the former being a little more intense. 

 Nor does he know of any striking difference in external 

 structure between the sexes, excepting the prominences 

 which become developed during the breeding season on 

 the front legs of the male, by which he is enabled to 

 hold the female." It is surprising that these animals have 

 not acquired more strongly marked sexual characters ; for, 

 though cold-blooded, their passions are strong. Dr. Q-unther 

 informs me that he has several times found an unfortunate 

 female toad dead and smothered from having been so closely 

 embraced by three or four males. Progs have been ob- 



« "Zoology of the Voyage of the Beagle," 1843. Bell, ibid., p. 49. 



*' "The Naturalist in Nicaragua," 18'74, p. 321. 



■" The male alone of the Bufo sikimmensis (Dr. Anderson, "Proc. Zoolog. 

 Soc," 1811, p. 204) has two plate-like callosities on the thorax and certain 

 rugosities on the fingers, which perhaps subserva the same end as the above- 

 mentioned prominences. 



