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Show 26 HEXU AL SELECTION. l' ,\1:'1' JJ. ('ould not fail to cat(·h tho 'YO of every passing cr atml('. Tho ·o colours may b 1 beneficial by ma,king thiH toad known to all l>irds of pr y as a uausoon mouthful; for it is familiar to every one that these animals emit a poisonous . ccretion, which causes the mouth of a <log to froth, ns if attacked by hydrophobia. 1 was the more struck with the conspicuon. · colonrs of this toad, as close by I found a lizard ( Proctotretus multimac~~lcdus) which, wh n frightened, :flattened its body, c1osed its eyes, and then from its mottled tints could hardly be clistinguishnl>lo from the surroumling sand. vVith respect to sexual diiTerenccs of colonr, Dr. Gi1n-ther knows of no striking instance with frog.· or totlds; yet he can often distinguish tho male from tho female, by the tints of the former l>cing a little more intense. Nor do ·s Dr. Gi.i.nthor know of any striking difference in external structure between the sexes, exccptiug the prominences which b'eeomc developed during the breeding- season on the front-legs of the male, by which he is enabled to hold the female. 'rho lVIegalophrys mon· icmct 41 (fig. 32) offers the best case of a certain amount of . -tructmal differenc between the sexes ; for in the male the tip of the nose aml the eyelids are produccu iuto trianguln,r flaps of skin, and there is a little black tubercle on the back-characters which arc absent, or only feebly developrd, in tho females. It il:l surprising that frogs and toacls should not have acquired more r;trongly-ma.rkecl sexual differences; for though oldblooded, their pa ions are strong. Dr. Gunther informs me tbat he has several times found an unfortunate female toad dead mHl smothered from having been so dosely embraced by three or four males. 11 'Tile Reptiles of I1ulio,' by Dr. A. Giinthcr, Tio.y Soc.l!:l(H, p. 413. CIIAP. Xll. Al\lPHIBIANS. 27 These animals, however, offer one interestino· sexual difference, namely in the musical powers poss~ssod by the males; but to speak of music, when applied to the discordant and overwhelming sounds emitted by male Lull-frogs a~d some o~her spec~es, seems, according to our taste, a smgularly mappropnate expression. Nevertheless certain frogs sing in a decidedly pleasing manner. Near Hio de Janeiro I used often to sit in the evening to listen to a number of little Hylre, which, Fig, 32. Megalophrys montana. The two left-hand figures, the male; the two rlght·hand figures, the fcmqlc. perched on blades of grass close to the water sent forth sweet chirping notes in harmony. The v~rious sound.s arc emitted. chiefly by the males during the breedmg-scason, as m the case of the croaking of our common frog.42 In accordance with this fact the vocal organs of the males are more highly developed than those of the females. In some genera the males alone 4z Bell, 'IIiotory of British Reptiles,' 1849, p. 93, |