422 SUMMARY OF CUUUENT KESEARCHES RELATING TO 



chapter lie detils with the aphorism " The uuclcar substaucc is the 

 fertilizing muteriiil, which starts the process of devclopmeut." Evi- 

 dence in support of this is to be found in the striking fact that through- 

 out the animal kingdom fertilization is efiected in essentially tlie same 

 way ; the direct result of the entrance of the spermatozoon is ordinarily 

 the innnediate j^recursor of embryonic division ; this again com- 

 mences with changes in the germinal nucleus, which arc only suc- 

 ceeded by changes in the protoplasm. An analysis of this process 

 shows us conclusively that the entrance of a spermatozoon into the egg 

 is not of itself sufficient f(jr fertilization, but is only the commence- 

 ment of the process ; this is well shown by an observation of Auerbach 

 on Ascaris nigrovenosa, where the two nuclei were seen to miss one 

 another, and i)ass into opposite halves of the cell ; shortly afterwards 

 the nuclei died. There is no reason for supposing that the tail of the 

 spermatozoon is anything more than a locomotor organ. Still more 

 instructive are the cases where the spennatozoon enters the egg-cell 

 before it is ripe ; here the male cell remains for a time unaltered, for 

 the process of development cannot begin till the ovarian nucleus is 

 formed, which is only after the extrusion of the polar globules. As 

 soon as this is effected there is a fusion of the cells. As Van 

 Beneden has rightly i)oiuted out, we must distinguish between the 

 cojnilation of the male and female cells, and the fusion of the nuclear 

 parts. 



The second chapter is entitled " The fertilizing substance is 

 also the bearer of peculiarities, which have been inherited by descen- 

 dants from their ancestors." Reference is made to Niigeli's distinction 

 between idio])lasm and nutrient protoplasm, and Hertwig tries to show 

 tliat the nuclei of the sexual products satisfy the requirements of 

 Nageli's hypothesis. It appears to be a true law of reproduction that 

 normal fertilization, which causes a regular development, is always 

 effected by a single spermatozoon. Nucleiu ap])ears to be the sul)- 

 stance which not only fertilizes but also inherits peculiarities. It 

 must not be forgotten that fertilization is not merely a chcmico-physical 

 l)rocess, but is also morphological, inasmuch as the nuclear part of the 

 spermatozoon unites with the nucleus of the egg to form a fresh nucleus. 

 C(mnecting the results of various observers, Hertwig concludes that 

 the head of the spermatozoon has been shown to be directly derived 

 from the nucleus of the spermatocyte, and that, in fertilization, it 

 directly passes into the sperm-nucleus. The derivation of the ovarian 

 nucleus frcmi the germinal vesicle is much more complicated, and the 

 process is difficult to fcjllow out in detail. At the same time it is clear 

 that the continuity of the nuclear generations is not broken ; there are 

 changes, but no new formations. " Omnis nucleus e nucleo." 



The discussion is thus summed up : the organization of the mother 

 and father is, in the act of reproduction, conveyed to the child by 

 organized substance of a very complex molecular constitution. In the 

 development of a chain of organisms there are no new formations, 

 there are no breaks ; in the successions of individuals there are only 

 changes in organization, whereby force is developed. The nuclei are 

 to be considered as the elements of complicated molecular structure 



