The physiology of reproduction / by Francis H.A. Marshall with a preface by Professor E.A. Schäfer ... and contributions by William Cramer ... and James Lochhead.

  • Marshall, F. H. A. (Francis Hugh Adam), 1878-1949.
Date:
1910
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Licence: Public Domain Mark

Credit: The physiology of reproduction / by Francis H.A. Marshall with a preface by Professor E.A. Schäfer ... and contributions by William Cramer ... and James Lochhead. Source: Wellcome Collection.

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    in the higher animals is less liable to modification than is the case with certain of the lower forms of life, there is abundant evidence that among the former no less than among insects the sexual functions are affected by external conditions and food supply. Darwin remarks that any sort of change in the habits of life of an animal, provided it be great enough, tends in some way to affect the powers of reproduction. “The result depends more on the constitution of the species than on the nature of the change ; for certain whole groups are affected more than others ; but exceptions always occur, for some species in the most fertile groups refuse to breed, and some in the most sterile groups breed freely.” “Sufficient evidence has now been advanced to prove that animals when first confined are eminently liable to suffer in their reproductive systems. We feel at first naturally inclined to attribute the result to loss of health, or at least to loss of vigour; but this view can hardly be admitted when we reflect how healthy, long-lived, and vigorous many animals are under captivity, such as parrots and hawks when used for hunting, chetahs when used for hunting, and elephants. The reproductive organs themselves are not diseased ; and the diseases, from which animals in menageries usually perish, are not those which in any way affect their fertility.” 1 It would seem probable that failure to breed among animals in a strange environment is due not, as has been suggested, to any toxic influence on the organs of generation, but to the same causes as those which restrict breeding in a state of nature to certain particular seasons, and that the sexual instinct can only be called into play in response to definite stimuli, the existence of which depends to a large extent upon appropriate seasonal and climatic changes.” There are at present no sufficient data for a comparative account of the physiology of breeding among the lower animals ; and in the present chapter, which is preliminary in character, I shall content myself with stating a few general facts about 1 Darwin, Variation of Animals and Plants, Popular Edition, vol. ii., London, 1905. 2 See especially page 20, where Bles’s observations on the breeding habits of Amphibia are referred to.