1064 



SUBMAMMALIAN VERTEBRATES 



in the fact that, as has been stated, the de- 

 veloping gonads of most fish pass through 

 an indifferent and then a bisexual stage. 

 In the latter phase, both ovarian and tes- 

 ticular elements are present and there is, 

 in effect, a transient and juvenile hermaph- 

 roditism. Subsequently, the gonad usually 

 becomes a testis or ovary. In exceptional 

 cases, functional gonadal tissue of both 

 sexes persists into adulthood (Table 17.1). 

 In Sargus and Serranus such hermaphrodit- 

 ism appears to be normal and frequent. In 

 many individuals of these genera, gross and 

 microscopic study has proven the co-exist- 

 ence of normal ova and sperm (van Oordt, 

 1930; van den Broek, 1933; Dantchakoff. 

 1936; D'Ancona, 19501. 



Hermaphroditism in Lebistes is not regu- 

 lar. However, functional bisexuality was ob- 

 served in 1 fish and in 18 of its young; 

 parent and offspring, although virgin and 

 individually isolated, bore young (Spurway, 

 1957 ) . Parthenogenesis was discarded as an 

 explanation in view of the co-existence of 

 functional testicular and ovarian tissue and 

 the likelihood of self-fertilization. The oc- 

 currence of the latter, although claimed in 

 other cases, seems not previously to have 

 been supported by the evidence; in Spur- 

 way's series self-fertilization seems proba- 

 ble. The offspring of the 18 fish, inciden- 

 tally, were almost all females. 



In a second type of hermaphroditism the 

 adult fish at first is morphologically of one 

 sex but subsequently undergoes sjiontaneous 

 reversal to the other. If the testis develops 

 first, the condition is known as protandry. 

 Cunningham (1886a) and Nansen (1887) 

 believed that Mijxine is usually a protan- 

 drous hermaphrodite, but Cole (1905) and 

 Conel (1917) were not convinced. Cole was 

 of the opinion that every adult Myxine has 

 "either a mature testis and a rudimentary 

 ovary, or a mature ovary and a rudimen- 

 tary testis." Hermaphroditism due to sex 

 reversal does occur during adulthood in 

 widely divergent teleostean genera (Table 

 17.1). It is significant that, wuth the excep- 

 tion of the doubtful case mentioned above, 

 all instances of spontaneous sex reversal 

 seem to be protogynous (ovary first, testis 

 later) rather than protandrous. 



Bullough (1947) has reviewed Liu's al- 



most inaccessible report (1944) on the Ori- 

 ental species Monoptenis javanensis, which 

 regularly "functions as a female during the 

 first half of its life and as a male during 

 the second." The same phenomenon is re- 

 ported for Pagellus (Gomez Larrafieta, 

 1953) and for Coris (Bacci and Razzauti, 

 1958). In C entropristes the males retain 

 ovarian, and the females testicular, tissue. 

 Age can be determined by examination of 

 the scales. The females are more numerous 

 in the younger age groups, but disappear by 

 the tenth year, whereas all fish surviving 

 during the next 10 years are males. On the 

 basis of this evidence, Lavenda (1949) be- 

 lieves that there may regularly be sponta- 

 neous female to male sex reversal after the 

 fifth year. Aoyama (1955) found that 22 of 

 3291 individuals of the yellow sea bream, 

 Taius tuniifrons, had hermaphroditic gon- 

 ads in which a transition from ovary to 

 testis was in jjrogress. Similar transforma- 

 tion was observed in 10 of 414 minnows 

 (Bullough, 1940b). 



Although exceptional, female to male sex 

 reversal has been described repeatedly and 

 in full detail for Xiphophorus (Essenberg, 

 1926; Harms, 1926b; Friess, 1933; Regnier, 

 1938). Before sex reversal the females give 

 birth to young; after reversal the newly 

 formed males demonstrate the completeness 

 of their transformation by successfully im- 

 pregnating virgin females. The oviduct is 

 converted to a sperm duct, male coloration 

 replaces that of the female, and the gono- 

 podium and characteristic "sword" develop. 

 No pathologic tissues have been found, a 

 point of possible significance, as develop- 

 ment of a testis in a hen, for example, is 

 known to follow tubercular destruction of 

 the functional ovary. Oviposition is arrested 

 and the female's characteristic "pregnancy 

 spot" (Trdchtigkeitsfleck) between the pel- 

 vic and anal fins fades. Then, as the gono- 

 podium and sword begin to grow, the ova 

 disappear, the follicles become atretic, and 

 most of the ovary disintegrates, leaving the 

 epithelium of the ovarian cavity. Leuko- 

 cytes eventually dispose of the masses of 

 ovarian debris. From the residual epithe- 

 lium radial sex cords rapidly proliferate to 

 form a testis, and germ cells multiply 

 quickly. Eventually the new testis is in- 



