THE DETERMINATION OF SEX 583 



to the egg-nucleus, and hence to the female line), and that 

 those which lack F are males. Sex-production in these 

 animals must therefore conform to the formulas 



Egg F + Spermatozoon G = FG, Female, 

 Egg G + Spermatozoon G = GG, Male. 



It is not known what is the exact relation between these 

 sex-chromosomes and those of the insects and nematodes. It 

 may be that F corresponds to X and G to Y — i.e., that the 

 female combination is XY and the male YY ; but there are 

 other possibilities. However this may be, it is evident that 

 the same principle appears in both cases. In both, one sex 

 is heterogametic, the other homogametic. In both, accordingly, 

 one-fourth of all the gametes are of different nuclear constitu- 

 tion from the others ; but in the insects these gametes (Y-class) 

 are confined to the male line, and are male-producing, while 

 in the sea-urchin the reverse relation exists. 1 



It is, of course, impossible to say in what measure the 

 foregoing conclusions will be found to hold true in other 

 animals and in plants ; but the convergence of cytological and 

 experimental results from widely separated groups leads us to 

 believe that the principle that they display is of wide validity. 

 The cytological evidence is now drawn from groups as far apart 

 as the insects, nematodes, and echinoderms ; and there is some 

 evidence that it may extend to the vertebrates on the one hand 

 (Vejdovsky, Guyer), and possibly even to the Protozoa on 

 the other (Schellack, Leger, and Duboscq), though both these 

 cases are doubtful. A wide and inviting field here lies open 

 to further observation ; and we may hope to see phenomena of 

 more or less similar type demonstrated in other groups where 

 they have hitherto escaped detection. It is probable, however, 

 that cytological differences as marked as those appearing in 

 the insects are exceptional, and that in many forms no visible 

 opceiebjL 2S exjsk Even in this case, however, the same principle 

 niay'rule, as is pointed out below. 



1 Beard, in his interesting paper on the determination of sex (in Zool.Jahrb. 

 Anat. Ont., 1902, 16), advanced the speculative view that the gametes were 

 primitively fourfold, including two kinds of eggs and two kinds of spermatozoa. 

 He assumed, however, that in all existing Metazoa one kind of spermatozoa has 

 become non-functional, and that sex is now determined solely by the egg. " The 

 spermatozoon has, and can have, absolutely no influence in determining the sex 

 of the offspring." This particular assumption was wrong, as is now apparent ; but 

 we should recognise the essential nucleus of truth in his conception, 



