66 THE EVOLUTION OF SEX. 



The research of Laulanie may now be referred to at greater length. As 

 the result of observations on the development of the reproductive organs in 

 the higher vertebrates, and especially in birds, he seeks to establish a strict 

 parallelism between the individual, and what he believes to have been the 

 racial history. In the chick, he distinguishes three main stages in the 

 development — (i) germiparity, (2) hermaphroditism, (3) differentiated 

 unisexuality. These he regards as recapitulating the great steps of the 

 historic evolution, (i.) For the first period of "germiparity," — from the 

 fourth to the sixth day, — the designation, sexual neutrality, or indifference, is 

 inappropriate, since the "cortical ovules" of the germinal epithelium have 

 from the first the precise morphological significance of female elements or 

 ova. In the female, they proceed by multiplication to form the ovary ; in the 

 male, they degenerate. (2.) The period of hermaphroditism begins with the 

 seventh day. In the male, the male ovules, from which the sperms are after- 

 wards developed, appear in the central tissue ; but at the same time cortical 

 or female ON-ules may be seen persisting. Similarly, in the developing ovary 

 of the female, the central or medullary portion, strictly separated by a par- 

 tition of connective tissue from the egg-forming layer, contains a large 

 number of medullary or male ovules. (3.) This hermaphroditism is of 

 short duration. The cortical or female ovules disappear from the testes by 

 the eighth or ninth day ; and the medullary or male ovules have by the 

 tenth day disappeared from the ovar}\ In regard to mammals, Laulanie 

 affirms, allowing some peculiarities, that the same three stages of germi- 

 parity, hermaphroditism, and unisexuality occur. 



Ploss has already been referred to as another investigator who maintains 

 the existence of embryonic hermaphroditism. Such also is the view held 

 by Professor Sutton, who concludes that both sets of organs are equally 

 developed up to a definite period, and emphasises the consequent necessity 

 for the hypertrophy of one sexual rudiment over the other. Only thus can 

 unisexuality be established. It ought perhaps to be noted, that hyper- 

 trophy is hardly a term strictly applicable to predominance of male over 

 female organs, since, in our contention, the whole nature of male organs or 

 elements is the physiological reverse of abundant nutrition. 



§ 3. Casual or Abnormal Hermapht-oditism. — In many species whicli 

 are normally unisexual, a casual hermaphrodite form occasionally presents 

 itself. The embryonic equilibrium or bisexuality — one of the two must in 

 a variable degree exist — is retained as an abnormality into adult life. 

 Even as far up in the organic series as birds and mammals, such casual and 

 yet true hermaphrodites occur. In most cases at least the result is sterility. 

 Among amphibians, which abound in reproductive peculiarities, herma- 

 phroditism exceptionally occurs, apart firom the one case {see below) where 

 it is known to be constant. The common frog, so much dissected in our 

 laboratories, has supplied several good illustrations. Thus Marshall notes 

 that the testes may be associated with genuine ova, or an ovary may occur 

 on one side, and a testis wdth an anterior ovarian portion upon the other. 

 Bourne gives a case of a frog with the ovary well developed on the right 

 side, and opposite this an ovary anteriorly replaced by testis. One of the 

 toads (^Pelobates fiisais') seems to be frequently hermaphrodite, the male 

 being furnished \dth a rudimentary ovary in front of the testes. A similar 

 hermaphroditism is not at all infrequent in cod, herring, mackerel, and 

 many other fishes ; while slightly lower do^^"n in the series, it occurs 

 in the hagfish (^AJyxine). Sometimes a fish is male on one side, female 



