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. The male alone of
the Bufo sikimmensis (Dr. Anderson, Proc. Zoolog. Soc. 1871, p. 204)
has two plate-like callosities on the thorax and certain rugosities on
the fingers, which perhaps subserve the same end as the above-mentioned
prominences.) It is surprising that these animals have not acquired
more strongly-marked sexual characters; for though cold-blooded their
passions are strong. Dr. Gunther 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. Frogs have been observed by
Professor Hoffman in Giessen fighting all day long during the
breeding-season, and with so much violence that one had its body ripped
open.
Frogs and toads offer one interesting sexual difference, namely, in the
musical powers possessed by the males; but to speak of music, when
applied to the discordant and overwhelming sounds emitted by male
bull-frogs and some other species, seems, according to our taste, a
singularly inappropriate expression. Nevertheless, certain frogs sing
in a decidedly pleasing manner. Near Rio Janeiro I used often to sit in
the evening to listen to a number of little Hylae, perched on blades of
grass close to the water, which sent forth sweet chirping notes in
harmony. The various sounds are emitted chiefly by the males during the
breeding-season, as in the case of the croaking of our common frog.
(48. Bell, History British Reptiles, 1849, p. 93.) 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 are provided with
sacs which open into the larynx. (49. J. Bishop, in Todd s Cyclopaedia
of Anatomy and Physiology, vol. iv. p. 1503.) For instance, in the
edible frog (Rana esculenta) the sacs are peculiar to the males, and
become, when filled with air in the act of croaking, large globular
378