FOUNDATION OF A THEORY OF HEREDITY. 189 



division usually accompanied by a typical form of indirect nuclear 

 division l . If any one is still in doubt upon this point, after the 

 observations of Fol and Hertwig, he might easily be convinced of 

 its truth by a glance at the figures (unfortunately too little known) 

 which Trinchese 2 has published, illustrating- this process in the eggs 

 of certain gastropods. The egg's of Ampkorina coerulea are in every 

 way suitable for observation, being entirely translucent, and having- 

 large distinct nuclei which differ from the green cytoplasm in 

 colour. In these eggs two polar bodies are formed one after the 

 other : and each of them immediately re-divides : hence it follows 

 that four polar bodies are placed at the pole of the eg-g. But how 

 is it that these four cells perish, while the nucleus, remaining in 

 the yolk and conjugating* with the sperm-nucleus, makes use of the 

 whole body of the egg and developes into the embryo ? Obviously 

 because the nature of the polar body is different from that of the egg- 

 cell. But since the nature of the cell is determined by the quality 

 of the nucleus, this quality must differ from the very moment of 

 nuclear division. This is proved by the fact that the supernu- 

 merary spermatozoa which sometimes enter the egg- do not con- 

 jugate with the polar bodies. According to Strasburger's theory, 

 the objection might be urged that the different quality of,the nuclei 

 is here caused by the very different quantity of cytoplasm by which 

 they are surrounded and nourished ; but on the one hand the small- 

 ness of the cell-bodies which surround most polar globules must 

 have some explanation, and this can only be found in the nature of 

 the nucleus ; and on the other hand the quantity of the cell-body 

 which surrounds the polar g-lobules of Ampkorina is, as a matter of 

 fact, somewhat larger than the sphere of green cytoplasm which 

 surrounds the nucleus of the egg ! The difference between the polar 

 bodies and the egg-cell can thus only be explained on the suppo- 

 sition that, in the division of the nuclear spindle, two qualitatively 

 different daughter-nuclei are produced. 



There does not seem to be any objection to the view that the 



1 According to the observations of Nussbaum and van Beneden, the egg of Ascaris 

 departs from the ordinary type, but I think that the latter observer goes too far 

 when he concludes from the form of the nuclear spindle (of which the two halves are 

 inclined to each other at an angle) that we have before us a process entirely differed 

 from that of ordinary nuclear division. i 



2 Trinchese, ' I primi moment! dell' evoluzione nei molluschi,' Atti Acad. Ly*' 

 (3) vii. 1879, Roma. * ae 



