192 CONTINUITY OF THE GERM- PLASM AS THE [IV. 



This point is so important that I must illustrate it by a few 

 more examples. The so-called polar bodies (to be treated more 

 in detail below) which are expelled during maturation from the 

 eggs of so many animals, are true cells, as was first proved by 

 Biitschli in Nematodes : their formation is due to a process of 

 undoubted cell-division usually accompanied by a typical form 

 of indirect nuclear division ^. 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 (un- 

 fortunately too little known) which Trinchese^ has published, 

 illustrating this process in the eggs of certain gastropods. The 

 eggs oi Amphorina coerulea are in every way suitable for obser- 

 vation, 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 ^gg. 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 ^g^, 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 supernumerary spermatozoa which 

 sometimes enter the egg do not conjugate 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 smallness 

 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 



^ According to the observations of Nussbaum and van Beneden, the 

 egg of A scans departs from the ordinary type, but I think that the latter 

 observer goes too far v^^hen 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 different from that of ordinary 

 nuclear division. 



'■' Trinchese, ' I primi momenti dell* evoluzione nei moUuschi,' Atti 

 Acad. Lyncei (3) vii. 1879, Roma. 



