SEX 371 



In the phyllopod crustacean, Simocephalusvetulus, Banta (1916) finds 

 that under certain experimental conditions " . . . the same individual, 

 even the same sex gland, may develop eggs and sperms at the same time or 

 sperms at one time and eggs at another time." Banta looks upon sex 

 as not a fixed or definite state but rather "a purely relative thing" 

 dependent upon the general physiological state of the organism which in 

 turn is under the influence of environmental factors. He also reports 

 sex intergrades in Daphnia longispina (1918). 



Lillie (1917a6c), as the result of a study of twins in cattle, concludes 

 that "sex-determination in mammals is zygotic, but it does not imply an 

 irreversible tendency to the indicated sex-differentiation. Intensification 

 of the male factors of the female zygote from the time of onset of sexual 

 differentiation by action of sex hormones may bring about very exten- 

 sive reversal of the indicated sex-differentiation" (1917c). 



Intersexes have recently been described in Drosophila simulans by 

 Sturtevant (1920). All the intersexual flies are modified females and 

 show the same grade of intersexuality. Sturtevant believes the condition 

 to be due to the action of a mutant gene. If this interpretation is 

 applied generally to the phenomenon of intersexuality it is evident 

 that certain genes at least are modifiable by environmental conditions, 

 for the reason that such conditions so often evoke the intersexual state. 



A very striking instance of the control exercised by environmental 

 factors over the sex of a given individual is found in Bonellia (Baltzer 

 1914). In this gephyrean worm the male is very small and degenerate, 

 and lives parasitically upon the long proboscis and in the nephridium 

 of the much larger female. If young individuals are kept in an aquarium 

 by themselves they develop into females, but if they are placed with 

 mature females they settle upon the probosces of the latter and develop 

 into males. By allowing them to remain on the probosces for varying 

 lengths of time Baltzer was able to obtain many intergrades between the 

 typical male and female conditions. It is plain that the proboscis 

 exercises an influence over the sex of the young animal, but whether this 

 is through a secretion or some other agency is not known. 



A somewhat similar case is that of Crepidula plana, described by 

 Gould (1917). This mollusk is hermaphroditic but completely protan- 

 dric, i.e., the male and female phases are entirely separate in time, the 

 former developing first. The development of the male phase is dependent 

 upon the presence of a larger individual (not necessarily a female) of the 

 same species. If a male is removed from the neighborhood of a larger 

 individual the male organs degenerate, and after a period of sexual 

 inactivity the animal becomes a female. The nature of the stimulus 

 exerted by the larger individual has not been ascertained. 



Plants. Experiments of a corresponding nature on sex modification 

 in plants are on the whole less conclusive than those on animals, for the 



