VI.] THEIR SIGNIFICANCE IN HEREDITY. 38 I 



forward the idea, even as a suggestion, when there was no secure 

 foundation for it. The morphological aspects of the formation 

 of the first and second polar bodies are so extremely similar 

 that such a supposition might have been considered as a mere 

 effort of the imagination. 



Hensen ^ also rejected the second part of the supposition that 

 reduction must take place in the number of the hereditary 

 elements of the (^gg^ and that such reduction is caused by the 

 expulsion of polar bodies, because he believed it to be incom- 

 patible with the fact, which had just been discovered, that polar 

 bodies are formed by parthenogenetic eggs. I le concludes with 

 these words : ' If this striking fact be confirmed, the hypothesis 

 which assumes that the (igg must be divided into half before 

 maturation, is refuted, and there only remains the rather vague 

 explanation that a process of purification must precede the 

 development of the embryo.' Nevertheless Hensen is the only 

 writer who has hitherto taken into consideration the idea that 

 sexual reproduction causes a regularly occurring 'diminution 

 in the hereditary elements of the ^gg' 



III. The Foregoing Considerations applied to the 



Male Germ-Cells. 



If the result of the previous considerations be correct, and if 

 the number of ancestral germ-plasms contained in the nucleus 

 of the egg-cell destined for fertilization must be reduced by one 

 half, there can be no doubt that a similar reduction must also 

 take place, at some time and by some means, in the germ- 

 plasms of the male germ-cells. This must be so if we arc 

 correct in maintaining that the young germ-cells of a new 

 individual contain the same nuclear substance, the same germ- 

 plasm, which was contained in the fertilized egg-cell from 

 which the individual has been developed. The young germ- 

 cells of the offspring must contain this substance if my theory 

 of the continuity of the germ-plasm be well founded, for this 

 theory supposes that, during the development of a fertilized 

 ^gg, the whole quantity of germ-plasm does not pass through 

 the various stages of ontogenetic development, but that a small 



^ Hensen, ' Die Grundlagcn dcr Vererbung nach dcin gcgcnwartigcn 

 Wissenskreis,' Zeitschr. f. wisscnschaftl. Landwirthschaft, Berlin, 1885. 



P- 731- 



