. The descent of man, and selection in relation to sex. Evolution (Biology); Sexual selection in animals; Sexual dimorphism (Animals); Sex differences; Human beings. &6 SEXUAL SELECTION. [Part II. fact the vocal organs of the males are more highly de- veloped than those of the females. In some genera the males alone are provided with sacs which open into the For instance, in the edible frog {liana esculen- ta) " the sacs are peculiar to the males, and become, when filled with air in the act of croaking, large globular blad-. Fig. 32.— Megalophrys raontana. The two left-hand
. The descent of man, and selection in relation to sex. Evolution (Biology); Sexual selection in animals; Sexual dimorphism (Animals); Sex differences; Human beings. &6 SEXUAL SELECTION. [Part II. fact the vocal organs of the males are more highly de- veloped than those of the females. In some genera the males alone are provided with sacs which open into the For instance, in the edible frog {liana esculen- ta) " the sacs are peculiar to the males, and become, when filled with air in the act of croaking, large globular blad-. Fig. 32.— Megalophrys raontana. The two left-hand figures, the male ; the two right-hand figures, the female. ders, standing out one on each side of the head, near the corners of the ; The croak of the male is thus rendered exceedingly powerful; while that of the female is only a slight groaning The vocal organs differ considerably in structure in the several genera of the family; and their development in all cases may be attrib- uted to sexual selection. Reptiles. Chelonia,—Tortoises and turtles do not offer well- marked sexual differences. In some species, the tail of 43 J. Bishop, in 'Todd's Cyclop, of Anat. and Phys.' vol. iv. p. 1503. 44 Bell, ibid. pp. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Darwin, Charles, 1809-1882. New York: D. Appleton and Company
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