388 ON THE NUMBER OF POLAR BODIES AND [VI. 



going into further details, and by critically examining the 

 numerous observations upon spermatogenesis which have now 

 been recorded. 



I will only mention that among the various nuclei and other 

 bodies in different animals which have been considered by 

 different observers as the polar bodies of the sperm-cells, or 

 the cells which form the latter — in my opinion the paranucleus 

 ('Nebenkern') of the 'spermatides' described by La Valette 

 St. George ^ has the highest claim to be considered as the 

 homologue of a polar body. But I am inclined to identif}' it 

 with the first rather than the second polar body of the egg-cells, 

 and to regard it as the histogenetic part of the nucleoplasm 

 which has been expelled or rendered powerless by internal 

 transformations. There are two reasons which lead me to this 

 conclusion : first, as I have tried to show above, it is probable 

 that the ancestral germ-plasms are not removed by expulsion, 

 but by means of equal cell-division ; secondly, my theory 

 asserts that the histogenetic nucleoplasm cannot be rendered 

 powerless until the close of histological differentiation. 



The whole question of the details of the transformations 

 undergone by the nucleus of the male germ-cells is not ready 

 for the expression of a mature opinion. From the very nu- 

 merous and mostl}^ minute and careful observations which have 

 been hitherto recorded, we cannot conclude with any degree of 

 certainty when and how the 'reducing division' of the nucleus 

 takes place, nor can we decide upon the processes which 

 signify the purification of the germ-plasm from the merely 

 histogenetic part of the nucleoplasm. But perhaps it has not 

 been without value as regards future investigation that I have 

 tried to apply to the male germ-cells the views gained from our 

 more certain knowledge of the corresponding structures in the 

 female, and thus to indicate the problems which now chiefly 

 demand solution. 



IV. The Foregoing Considerations applied to Plants. 



It remains to briefly consider the case of plants. Obviously, 

 the 'reducing division' of the germ-nuclei, if it takes place at 



' La Valette St. George, * Ueber die Gcnese der SamcnkOrper.' 

 Fiinftc Mitthcilung. Die Spermatogencse bci den Saugelhieien und 

 dem Mcnschcn, Archiv f. mikrosk. Anat. Bd. XV. 1878. 



