No. 542] SHORTER ARTICLES AND DISCUSSION 109 



acted ? The evidence that sex is regulated by an internal mech- 

 anism has become so strong in recent years that until the action 

 of the environment is made clear one may well hesitate to accept 

 the case as showing that sex is actually changed or produced by 

 an external agent. Curiously enough, every one seems to have 

 overlooked still another possibility that may solve the difficulty. 

 The delay in the fertilization may cause the polar spindle to stick 

 to the surface of the egg so that it fails later to take part in the 

 development, in which case the sperm nucleus alone would pro- 

 duce the nuclei of the embryo. Or, on the other hand, the delay 

 may cause the early stages in the formation of the female pro- 

 nucleus to progress so far that after fertilization the sperm nu- 

 cleus may be excluded in part or entirely from the development. 

 In either case the presence of a single nucleus would be expected 

 to give rise to a male. It is significant in this connection that 

 the changes described by King that affect the sex-ratio of the 

 frogs' eggs produce a higher percentage of males. 



There is another curious fact in relation to sex-determination 

 in the frog. Pfliiger described a high percentage of hermaph- 

 rodites amongst the tadpoles. Kuschakewitsch has given a de- 

 tailed account of the development of the hermaphroditic glands. 

 Most or all of these organs are later transformed into testis. 

 In general it may be said that eggs from a pair give either equal 

 numbers of males and females; or a mixture of males, females, 

 and hermaphrodites; or all hermaphrodites (potentially males). 

 It is possible that the pseudo-hermaphroditic condition may be 

 connected with the failure of one of the two pronuclei to take 

 part in the development. 



If the explanation that I have suggested is correct we might 

 expect to find evidence in its support from the number of chro- 

 mosomes in the tadpoles that develop from these late fertilized 

 eggs. This would be expected if it is the male pronucleus that 

 gives rise to the nuclei of the embryo. But if it is the female 

 pronucleus that is responsible for the result, the number of chro- 

 mosomes in the cells of the embryo might be haploid or diploid 

 depending on whether the second polar body was, or was not 

 given off. At any rate, this suggestion should be put to the 

 test of observation before we conclude that sex may be deter- 

 mined by external agents. If the view here suggested prove 

 true, sex is still determined by an internal factor in the same 

 sense that the sex of the bee's egg is determined by the presence 

 of one or of two pronuclei. T- H. Morgan 



