THEIR SIGNIFICANCE IN HEREDITY. 353 



parthenogenetic as well as in sexual eggs. A part of the nucleus 

 must thus be removed from both kinds of eggs, a part which was 

 necessary to complete their growth, and which then became super- 

 fluous and at the same time injurious. In this respect the observa- 

 tions of Blochmann J upon the eggs of Musca vomitoria seem to me 

 to be very interesting. Here the two successive divisions of the 

 nuclear spindle arising from the egg-nucleus take place, but true 

 polar bodies are not expelled, and the two nuclei corresponding to 

 them (one of which divides once more) are placed on the surface of 

 the egg, surrounded by an area free from yolk granules ; and they 

 break up at a later period. The essential point is obviously to 

 eliminate from the egg-cell the influence of nucleoplasm which has 

 been separated from the egg-nucleus as the first polar body; and 

 this condition is satisfied whether the elimination is brought about 

 by a process of true cell-division, as is the rule in the eggs of most 

 animals, or by the division and removal of part of the egg-nucleus 

 alone. The occurrence of the latter method of elimination cer- 

 tainly constitutes a still further proof of the physiological im- 

 portance of the process, and this, taken together with the uni- 

 versal occurrence of polar bodies in all eggs parthenogenetic and 

 sexual forces us to conclude that the process must possess a 

 definite significance. No one of the various attempts which have 

 been made to explain the significance of polar bodies generally 

 is applicable to the first polar body except that which I have 

 attempted. 



But the case is different with the significance of the second 

 nuclear division, or the second polar body. Here it might perhaps 

 be possible to return to the view brought forward by Minot, 

 Balfour, and van Beneden, and to consider the removal of this 

 part of the nucleus as the expulsion of the male part of the pre- 

 viously hermaphrodite egg-cell. The second polar body is only ex- 

 pelled when the egg is to be fertilized, and at first sight it appears 

 to be quite obvious that such a preparation of the egg for fertilization 

 must depend upon its reduction to the female state. I believe how- 

 ever that this is not the case, and am of opinion that the process 

 has an entirely different and much deeper meaning. 



How can we gain any conception of this supposed herma- 

 phroditism of the egg-cell, and its subsequent attainment of the 



1 1. c., p. no. 

 A a 



