Archive image from page 39 of The descent of man, and. The descent of man, and selection in relation to sex descentofmansel02darw Year: 1871 26 SRXUAL SELECTION. [Pakt II. fact the vocal organs of the males are more highly de- veloped than those of the females. In some genera the males alotoe are provided with sacs wliich open into the larynx.' For instance, in the edible frog {Rana esculen- ta) ' the sacs are peculiar to the male., and become, when filled with air in tlio act of croaking, large globular blad-

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