16 Mr Hichso^i, On the fragmentation [Nov. 14, 



other than those derived from pre-existing nuclei. It will require 

 at any rate rather much stronger evidence than we have at 

 present to induce naturalists to believe in "free nuclear forma- 

 tion." 



The facts that have been observed then — not only in Musca 

 but also in Pieris, Pyrrochoris and Lasius by Henking, in Phry- 

 ganids by Patten, and by Tichomiroff in the silkworm — can only 

 be interpreted on the lines either that the first divisions of the 

 oosperm nucleus are regular karyokinetic figures and have been 

 missed, or that the nucleus fragments into small particles, too 

 small to be recognised with any decree of certainty, which are dis- 

 tributed through the substance of the ovum, and give rise to the 

 so-called free-nuclei. 



It seems to me to be highly improbable that these first spindles 

 could have been missed by so many careful observers if they really 

 occurred ; for the spindles in the formation of the polar bodies 

 and in the later stages of nuclear division are to be made out 

 without much difficulty and seem to be of regular occurrence. 



Lastly, I may say that I have already described and figured the 

 fragmentation of the nucleus of the fertilised ovum of Millepora, an 

 ovum that does not segment, and that I failed in the case of 

 AUopora, as in Distichopora, to follow the nuclear changes imme- 

 diately following the fertilisation of the ovum. 



Now it will be observed that in all these cases segmentation 

 of the cell substance of the egg does not occur immediately after 

 fertilisation. 



In holoblastic eggs, such as Amphioxus, Echinus, Peripatus 

 capensis and many others, well-marked karyokinetic figures can 

 be seen on the first division of the segmentation nucleus, and also 

 in those meroblastic ova in which evidence of cell formation — that 

 is to say, of the drawing together of the protoplasm into blocks — 

 occurs immediately after fertilisation as in Cephalopods (Vialleton), 

 Anguis fragilis (Oppel), Tubularia (Tichomiroff), and others. 



In the case of Aphis there is, as Will observed, a distinct 

 accumulation of the protoplasm round the nuclei, although there 

 is no segmentation. 



It seems to me to be probable then that the formation of 

 karyokinetic figures may be in some manner connected with the 

 regular cell formation, but that in cases where cells are not imme- 

 diately formed nuclei may divide amitotically. Or in other words, 

 that the force, whatever it may be, that initiates cell formation 

 drags the nuclei into spindle figures, etc. 



How are these views supported by other facts of histology? 

 When the cells are commencing to be formed in Elasmobranch 

 embryos we find spindles, and also in the formation of polar 

 bodies. 



