Chap. XII. Amphibians. 349 



" beneath, which in the spring becomes a rich bright orange, 

 " marked everywhere with round dark spots." The edge of the 

 crest also is then tipped with bright red or violet. The female 

 is usually of a yellowish-brown colour with scattered brown 

 dots, and the lower surface is often quite plain. 44 The young 

 are obscurely tinted. The ova are fertilised during the act of 

 deposition, and are not subsequently tended by either parent. 

 We may therefore conclude that the males have acquired their 

 strongly-marked colours and ornamental appendages through 

 sexual selection ; these being transmitted either to the male 

 offspring alone, or to both sexes. 



Anura or Batraehia. — "With many frogs and toads the colours 

 evidently serve as a protection, such as the bright green tints 

 of tree-frogs and the obscure mottled shades of many terrestrial 

 species. The most conspicuously- coloured toad which I ever 

 saw, the Phryniscus nigricans* 5 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 pass- 

 ing creature. These colours 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 4;> 

 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 colour, Dr. Gunther 

 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. 47 It is surprising that 



44 Bell, ' History of British Rep- sihimmensis (Dr. Anderson, * Proc. 

 tiles,' 2nd edit. 1849, pp. 146, 151. Zoolog. Soc.,' 1871, p. 204) has two 



45 'Zoology of the Voyage of the plate-like callosities on the thorax 

 * Beagle," ' 1843. Bell, ibid. p. 49. and certain rugosities on the ringers, 



46 ' The Naturalist in Nicaragua,' which perhaps subserve the same end 

 .874, p. 321. as the above-mentioned prominences, 



47 The male alone of the Bvfo 



