Beard, Heredity and thc Cause of Variations. 3G7 



one will lall tbe lot of devcloping int(3 an onibryo, wliile the other 

 will furniöh the sexual pioducis of this. Tiie two cells are in all 

 respects similar and eqiiivalent, so mucli so, tliat if bolli loiin em- 

 bryos these are identical twins. In the ancestry neither cell liad 

 ever been a higher aninial, neither they nor their ancestors liad 

 ever formed parts of an aninial body. But this ancestry is con- 

 tinuous with a long line of germ-cells, and at regulär intervals 

 these were exactly like certain sister-cells, whicli did develop and 

 form individuals. Although one of the two does not develop, it 

 retains for itself and also l'or all its immediate progeny in the 

 meantime all the properties or characters of the other, which were 

 it or any of its progeny to develop would make it or them iden- 

 tical twins with the other. This is the greatest wonder in em- 

 bryology! As Wallace has said, the foundation of the Darwinian 

 Theory is the variability of species. It does not attempt to explain 

 the cause of Variation, but starts from the fact of its existence. 

 Under this theory resulting from the struggle for existence there 

 is a survival of the littest. But the existence of factors far more 

 potent for the elimination of individuals than natural selection may 

 be insisted upon. Thus, it can be shown, that of the male indi- 

 viduals of the human race certainly one-third, and probably very 

 nearly one-half, are eliminated before birth. The only adequate 

 cause of Variation yet suggested is Weismann's germinal selection. 

 This is purely a mental concept, in its nature it is very compli- 

 cated, and being quite w^ithout connection with any known pheno- 

 menon or epoch of the development, it hangs entirely in the air. 

 As defined by Weismann, the process would furnish a very great 

 variety of gametes or conjugating cells, and these would be so 

 varied in their characters or qualities, that the resemblances rather 

 than the diiferences among the progeny would require explanation. 

 Germinal selection, as conceived of by Weismann, is too hypo- 

 thetical and at the same time proves too much. The problem of 

 the cause of genetic Variation belongs to embryology. For various 

 reasons every egg or sperm must be regarded as containing 

 one complete set of all the characters or qualities necessary 

 to form an individual of the species. At fertilisation two sets of 

 these are somewhat loosely joined together. In the developing 

 embryo only one complete set of characters is made use of, and, 

 white the other corresponding qualities remain more a less dor- 

 mant in its cells, that set or pack actually employed may be made 

 up of any characters taken from either of the two packs, but so 

 as to make up one complete pack. Turning then to the germ-cells, 

 each of these possesses the duplicated set, and later on at the so- 

 called „reduction" i. e., at the final division of the oogonia into 

 Gocytes, and of the spermatogonia into spermatocytes, prior to the 

 formation of conjugating cells or gametes, the twofold set becomes 

 diminished to one pack only by the elimination of one complete 

 pack. The true meaning of the reduction of chromosomcs is the 

 elimination of one set of characters or qualities, such that if among 



