550 THE POPULAR SCIENCE MONTHLY 



dieciousness must be regarded as unit characters, since they behave in 

 crossing according to Mendelian laws. Hermaphroditism probably 

 has its chromosome determinant as also dieciousness, hence the cyto- 

 logical study of the germ cells of hermaphrodite forms will hardly sup- 

 ply the clue to the cause of sex as it was until recently believed to do. 



In those insects where there is a dimorphism of spermatozoa, con- 

 sisting in the presence of an accessory chromosome in one half of the 

 gametes, no obvious diiference appears among the eggs. There are no 

 real grounds for a division of the ova into those with male character 

 and those with female character. In the light of Correns's recent ob- 

 servations, the eggs had better all be regarded as possessing the same 

 sex tendency, and this probably female in nature. The spermatozoon 

 with the accessory chromosome need then only be thought of as pos- 

 sessing the female tendency, and the one that lacks it, as possessing 

 the male tendency, and the facts are brought into line with the results 

 of Correns and admit of the same interpretation. In the case where 

 large and small eggs are produced, as by Dinophilus apatris, it is con- 

 ceivable that there is selective fertilization, i. e., while both tvpes of 

 egg may be female in tendency, only the larger admit of fertilization 

 by a female-producing spermatozoon. 



The present status of the case concerning the determination of sex, 

 as well supported for a large class of plants and animals, appears to be 

 that sex is determined by the spermatozoa (or pollen grains) — which 

 are male and female in the proportion of 1 : 1 — and at the instant of 

 fertilization. But surely it would be the utmost folly to hold on the 

 basis of so comparatively few facts, that this explanation applies uni- 

 versally. Nature arrives at similar ends by devious and divers ways 

 and it is not inconceivable that sex has been attained by several paths, 

 and is now determined in different modes and at different times in the 

 different groups of animals and plants. 



