158 SCIENCE PROGRESS. 



evolved during the course of cellular ontogeny. On the 

 other hand the nucleus and cytoplasm, as such, are never 

 so evolved. Their relative proportions may increase or 

 diminish without limit, but they neither arise de novo, nor are 

 they ever entirely suppressed, themselves constituting the 

 raw material out of which any future structural complexity is 

 evolved. Until lately, the difference of structure apparent 

 in the presence of the nucleus and cytoplasm was the only 

 cellular organisation of which anything definite was known, 

 and as both these constituents are typically persistent, it 

 became customary to regard cell-organs as things always 

 arising directly by fission from pre-existing similar struc- 

 tures. In other words, we have acquired the habit of 

 regarding persistence as characteristic of cellular organs. 

 No sooner, therefore, was the presence of spheres demon- 

 strated than the question presented itself — Do these struc- 

 tures arise by division from pre-existing spheres, or can 

 they, unlike the prime factors, be evolved during cellular 

 ontogeny? And though this question of their origin is of 

 the utmost importance, it appears to me that with respect to 

 the nature of the spheres as cell-organs it has in reality 

 nothing whatever to do. 



It remains then to determine if possible whether the 

 spheres (quite apart from their character as organs of the 

 cell) have thus an evolved or persistent nature. How do 

 they arise in the sexual elements ? Are they persistent, but 

 restricted to the male, dying out in the ova ; persistent, but 

 restricted to the female, dying out in the spermatozoa ? Or 

 do they arise from both, and fuse in the egg like the nuclei 

 in the formation of a completely fertilised cell ? 



Finally, can these organs ever be formed anew, and so 

 lose their claim to persistence and a place among the prime 

 factors of the cell ? 



Van Beneden regarded the spheres as arising simul- 

 taneously, immediately after the entrance of the spermato- 

 zoa into the egg : " Les deux spheres apparient simultane- 

 ment, si parfois on croit n'en voir qu'une, cela depend de la 

 position relativedesdeuxorgansrelativement al'observation". 

 In this case they do not appear to be present at the outset 



