98 THE ORIGIN OF GYNANDROMORPHS. 



tible of similar modifications, according to whether they remain free or 

 become parasitic on a female. 



The conditions in Crustacea and molluscs seem to show that, in 

 some cases at least, the animals are essentially hermaphrodites and 

 that external conditions and age are important factors in determining 

 the sex of the individual. These cases recall the phenomena shown by 

 many flowering plants where at one stage or under certain conditions 

 the male organs develop, under other conditions the female organs. 

 If in such cases sex-determining genes are present, their influence may 

 be readily overcome by external agencies or by age itself, which is in a 

 sense a condition in which some part of the body (through its output) 

 acts as an external agent to other parts. 



GYNANDROMORPHS IN ECHINODERMS. 



Cue* not (1898) and Delage (1902) described each a mature starfish 

 (Asterias glacialis) that had small patches of testis (with sperm) in 

 the ovary, and Buchner (1911) has recorded a similar case. Herlandt 

 has recently described a sea-urchin (Paracentrotus) that had three 

 normal and one "dark" testes and a large ovotestis with functional 

 ova and sperm. Artificial fertilization with the products of this ovo- 

 testis was successful, and the larvae were normal. Since Tennant has 

 shown for the sea-urchin that the female is homozygous and the male 

 heterozygous for the X chromosome, these cases can be easily explained 

 on the hypothesis of elimination of an X chromosome the resulting 

 parts being male. 



GYNANDROMORPHS IN VERTEBRATES. 



The group of vertebrates shows as a rule sharp separation into two 

 sexes, but the evidence relating to the factors involved is often so 

 little known that the group as a whole is difficult to handle. In one 

 subdivision, the birds, the female is the heterogametic sex with regard 

 to sex chromosomes, while in mammals, certainly in man, it is the male 

 that is heterogametic. The contrast here is the same as that in insects, 

 where the moths resemble the birds and the flies man. In some of 

 the lower groups there are evidences of hermaphroditism or of transi- 

 tory sex conditions. It becomes necessary, therefore, to take up the 

 different groups independently. 



GYNANDROMORPHS IN FISHES. 



Myxine, according to Cunningham and Nansen, is male when young 

 and later becomes female. In the young the anterior portion of the 

 testis is male, the posterior female; the testicular part atrophies after 

 it has functioned as a testis. But the later results of the Schreiners 

 indicate that while young Myxine is a true hermaphrodite as far as 

 the histological structure of the glands is concerned, it is not so func- 



