MENDELTSM AND SEX 197 



the functions of an accessory chromosome cannot be of 

 such general application as is claimed. 1 The existing evi- 

 dence applies largely to one group of insects. For some 

 members of this group, however, the evidence seems fairly 

 strong that the chromosomes in half the sperms differ from 

 those in the other half, and that in which sex is produced 

 depends upon which class of sperm has fertilised the mature 

 ovum. This theory will be considered again later. 



Accepting Wilson's theory, attempts have been made to 

 show that it corresponds to the Mendelian mode of transmis- 

 sion, and that sex is in fact a Mendelian character. Some of 

 these attempts have been controverted by Wilson himself. 



" This interpretation has been worked out in three forms, 

 which exhaust the a priori possibilities. These are, first, 

 that both sexes are sex-hybrids or heterozygotes 2 (Castle) ; 

 second, that the male alone is a heterozygote, the female 

 being a homozygote recessive (Correns) ; third, that the 



1 Foot, K., and Strobell, E. C., " The Nucleoli in the Spermatocytes and 

 Germinal Vesicles of Euchistus variolarius," Kiol. Bull., vol. xvi., 1909; Arnold, 

 G., "The Nncleolus and Microchroniosomes in the Spermatogenesis of Hydro- 

 philus pieeus," Archiv fur Zcllforschuny , ii. 1, 1908 ; Farmer and Moore, "The 

 Meiotie Phase (Reduction Division), in Animals and Plants, 1 ' Quart. Journ. 

 Micro. Science, vol. xlviii., Part IV., 1905. Foot and Strobell say (1909), with 

 regard to the work of Lefevre and M'Gill : (1) In her first work on this form 

 (1904), in which she expresses her indebtedness to Professor Lefevre, she found 

 no evidence of a chromatin micleolus in the resting spermatocyte. She and 

 Lefevre now find, in the same material, a chromatin nucleolus persisting through 

 the resting spermatocyte. (2) In her earlier work M'Gill identified the micro- 

 chromosome as the accessory chromosome. She and Lefevre now identify, in the 

 same material, one of the larger spermatogonial chromosomes as the accessory 

 chromosome. (3) In her original count of the spermatogonial chromosomes, 

 M'Gill found an even number, 28. She and Lefevre now find, in the tame 

 material, an odd number, 27 spermatogonial chromosomes. In view of these 

 contradictions we may justly hesitate to accept as definite the recent conclusions 

 reached by M'Gill and Lefevre in Anasa tristis, believing a new point of view 

 may give us still further variations in their very interesting observations. 



2 A "zygote" is the product of the fusion of two gametes. "Heterozy- 

 gote " is the Mendelian word for a zygote made up of two gametes, each bearing 

 the opposites in a pair of Mendelian characters (one the dominant, the other the 

 recessive). A heterozygote is in fact an impure dominant. A "homozygote" 

 is a zygote in which both gametes contain the same Mendelian character, both 

 dominants or both recessives. Extracted dominants or extracted recessives are 

 called homozygotes. 



