62 



SCIENCE 



[N". S. Vol. XXIX. No. 732 



that the eggs are determined as females by 

 their combination with the spermatozoa, 

 and that fertilization may here be con- 

 sidered as the immediate determining cause 

 of the female sex. In the bees and other 

 social Hymenoptera this conclusion is still 

 more probable, even though the Dzierzon 

 theory fall short of a complete demonstra- 

 tion. But this does not yet touch the root 

 of the matter. It is more than possible 

 that even in organisms that are incapable 

 of parthenogenesis the unfertilized egg 

 may in itself bear a sexual "tendency" 

 which would cause it to develop into a male 

 or female could parthenogenesis take 

 place. This is shown by the bees and ants 

 where the unfertilized sexual eggs produce 

 males, and the conclusion seems unavoid- 

 able that all bear the male tendency. Both 

 here and in the rotifer (if Maupas's con- 

 clusion be correct) the innate tendency of 

 the egg is male ; but this is not a fixed pre- 

 determination since it is reversed or sup- 

 pressed by fertilization. 



v. MENDELIAN THEORIES OF SEX-HEREDITT 



We are thus brought to the central prob- 

 lem of sex-production, namely, the nature 

 of the sexual tendencies of the gametes and 

 their interaction. Can sex be treated as a 

 form of Mendelian heredity, in which the 

 gametes bear male and female tendencies 

 or factors that correspond to those which 

 represent the dominant and recessive mem- 

 bers of a pair of allelomorphs? Should 

 we think of maleness and femaleness as 

 due to the presence in the egg of specific 

 male and female determinants that disjoin 

 in maturation and reeombine in fertiliza- 

 tion? That sex may be such a phe- 

 nomenon was first suggested by Stras- 

 burger, and the conception has since been 

 more fully developed, first by Castle and 

 afterwards by Correns and Bateson, each 

 in his own way. There are many facts 

 that seem to speak in its favor. Bach sex 



seems to show indications of the presence 

 of the opposite sex in a latent or recessive 

 condition. In hermaphrodites both sexes 

 are present in the active state and may 

 either appear side by side or may dominate 

 successively. In diecious forms there 

 seems to be no escape in certain cases from 

 the conclusion that opposite sexual tend- 

 encies disjoin in the maturation divisions. 

 One of the best examples of this is given 

 by the diecious mosses, already referred to. 

 As the Marchals's work shows, each spore 

 and all of its products is irreversibly pre- 

 determined as male-producing or female- 

 producing, and spores of both kinds are 

 found in the same capsule. It would seem, 

 therefore, that the two tendencies must be 

 brought together in fertilization; and we 

 should expect to find that the zygote or its 

 products (the sporogonium) should com- 

 bine the two. Such is indeed the fact. 

 Moss plants (gametophytes) formed by re- 

 generation from the stalk or wall of the 

 sporogonium are either actually hermaph- 

 rodite or produce hermaphrodites in a suc- 

 ceeding generation (again formed by re- 

 generation) — a condition never found in 

 the normal gametophj^tes developed from 

 the spores. But since the spores, formed 

 by the two maturation divisions from the 

 mother cells in the sporogonium, are again 

 strictly male-producing or female-produ- 

 cing, the sexual tendencies must be dis- 

 joined by these divisions. Translating 

 this into cytological terms, cells that con- 

 tain only a single or haploid series of 

 chromosomes bear but one tendency, male 

 or female; while those that contain the 

 double or diploid series bear both tend- 

 encies. The same appears to be true in the 

 liverworts (ilarchantia) according to the 

 observation of Noll and Blakeslee. 



With this the facts in the aphids and 

 similar cases, as far as they go, seem to 

 be in essential agreement. The summer 

 parthenogenetic eggs form but one polar 



