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Show 1886.J MR. J. B. SUTTON ON ATAVISM. 555 prostate an unimpeachable witness of an ancestry with the feathered tribe, low down among the oviparous reptiles. Let me now proceed to show how very little information we possess concerning latent germs which may be present in the embryo. For example, the discovery of the germ of an os centrale in the carpus of man was certainly startling. Yet its existence might have been anticipated from what we know of the variations in the number of the carpal ossicles in the adult. Atavism drew the attention of anatomists to a secondary astragalus in the human tarsus, and Barde-leben succeeded in detecting the germ. (This has been questioned by Baur, but his objections are inconclusive.) W e must now consider some cases of a different character. Atavism in relation to Secondary Sexual characters. As Darwin points out \ two distinct elements are included under the term "inheritance"-the transmission and the development of characters. The distinction is a most important one, especially in its bearing on the question of Atavism, that the two conditions will be illustrated by concrete examples. In most species of the Deer tribe it is the rule for the male alone to possess antlers, yet it is a well attested circumstance that under certain diseased conditions of the sexual organs, especially atrophy or degeneration of the ovaries, rudimentary horns which are never shed appear in the female. This shows us that although the female is in possession of the secondary sexual organs in virtue of transmission, vet they remain latent as a rule, and only become developed under extraordinary circumstances. The same holds good for those cases of hens who for years lay eggs, yet eventually cease to do so, put on one side the plumage proper to their sex, and adopt more or less completely the plumage of the cock. These examples open up the subject of secondary sexual characters. The question of primitive hermaphroditism has been already discussed in a preceding paper, and an attempt was made to show that, for a brief period at least, the embryo presents sexual parts common to the male and female, so that for a time it is absolutely impossible to determine the sex. What is true of the embryo applies equally to animals normally hermaphrodite : no distinctive characters are displayed externally. Also in cases of hermaphroditism occurring in animals normally bisexual, the secondary sexual characters are intermediate to those of the functional male and female. It is therefore fairly evident that the female, though she differs from the male in the non-development of secondary sexual characters, yet possesses them in a latent condition ; or, to put the matter briefly, they are transmitted, but not developed. This raises two questions, each of equal importance :-(1) H o w are these characters transmitted? (2) What hinders their development'? It seems to me that the second of these questions is the one with which we are chiefly concerned here, and that the non- development of 1 ' Descent of Man,' 2nd ed. p. 227. |
