1062 



SUBMAMMALIAX VERTEBRATES 



at hatching. The testis, clearly recognizable 

 as such, contains sex cords with numerous 

 germ cells and is invested with a thin 

 coelomic epithelium. The ovary is also well 

 differentiated, consisting of outer cortex 

 and central medulla. The two components 

 are clearly delimited. Most of the germ cells 

 are in the cortex. The metanephros is well 

 developed. Both sexes have mesonephric 

 ducts, but Miillerian ducts are present only 

 in the female. The development of the re- 

 productive tract in Anolis is similar, al- 

 though in this genus the Miillerian ducts 

 may persist after hatching in the male 

 (Forbes, 1956). 



Probably the earliest study of the em- 

 bryology of the snake's gonads was that 

 of Rathke (1839). Hartley's modern (1945) 

 account calls attention to the brief and 

 early (16th to 19th day) i)eriod of sex- 

 ual differentiation in the garter snake 

 and to the relative scarcity of heterosexual 

 vestiges at birth. Both phenomena ap- 

 parently are unique for the snake among 

 reptiles. 



The writer (Forbes, 1940a) has described 

 the embryology and post-hatching develop- 

 ment of the gonads, adrenal cortex, and 

 Miillerian duct of the alligator, Alligator 

 mississippiensis. Prolonged indifferent, bi- 

 sexual, and sexually differentiated stages 

 much like those reported in the turtle by 

 Risley (see above) were observed. A period 

 of pronounced bisexuality is succeeded by 

 sexual differentiation, but heterosexual 

 structures regularly persist until well after 

 hatching. The degree of adult bisexuality 

 is unknown, but the male alligator 18 

 months after hatching still has irregular 

 patches of cortex (potential ovarian tissue) 

 on his testis. The male Miillerian ducts are 

 fully formed at hatching, and their anterior 

 extremities may still be present 18 months 

 later. Females at this age and earlier have 

 in the posterior third of each gonad a solid 

 mass of medullary cords (potential semi- 

 niferous tubules ) similar to those seen in the 

 embryonic testis, but lacking germ cells. 

 A mesonephros and mesonephric duct are 

 always present. Thus again there is a con- 

 siderable retention of heterosexual struc- 

 tures. 



XXII. Spontaneous Adult 



Herniaphrotlitisni and 



Sex Reversal 



Fish 



Aristotle recognized hermaphroditism in 

 the channe, a perch-like form, and in two 

 other varieties (Thompson, 1910), as did 

 Ovid (Ovidius Naso, 1911). All three fish 

 are thought to have been serranids (Du- 

 fosse, 1856; Thompson, 1910). The classical 

 writers apparently shared the popular belief 

 that the fish are herma])hroditic because all 

 specimens caught contained eggs, i.e.. no 

 males were ever seen. A chapter title in a 

 book by Guilaume Rondelet (1558) con- 

 cerns fish "which give birth without the 

 assistance of the male," evidently a refer- 

 ence (the text is not enlightening) either to 

 hermaphroditism or to parthenogenesis. Du- 

 fosse (1856) states flatly that in three 

 serranid species the same fish which lays 

 the eggs also fertilizes them. 



Cavolini (1792) found ovotestes in the 

 Potsch and Blutstrieme] there is reason to 

 think that these were two of the fish about 

 which Aristotle had conmiented. Yarrell ex- 

 hibited to the Zoological Society of London 

 in 1845 a herring "having a lobe of female, 

 or hard roe, on one side, and a lobe of male, 

 or soft roe, on the other." The note adds that 

 the same phenomenon had been seen in 

 several other kinds of fish. In the 1880's a 

 friend of Carl Vogt, the German naturalist, 

 was about to eat a smoked herring when he 

 noticed that the reproductive tract was ab- 

 normal. The friend carefully removed the 

 tract, sent it to Vogt with a letter, and, one 

 hopes, ate the rest of the herring. In spite 

 of the unconventional fixation of the tissues 

 it was possible to confirm histologically that 

 both gonads were ovotestes; in addition, an 

 excretory duct on each side was so arranged 

 as to carry off both sperm and ova (Vogt, 

 1882). 



A number of examples of adult hermaph- 

 roditism are summarized in Table 17.1. Ad- 

 ditional references and details may be found 

 in books by Gemmill (1912) and Dean 

 (1923) and in D'Ancona's article (1956). 

 Two types of adult hermaphroditism can 

 be recognized. The basis for the first lies 



