I. 



Cell-Division. 



PART II. 



IN the number of Natural Science for January of this year an 

 attempt was made to give a more or less up-to-date account of 

 the karyokinetic method of cell-division. The present article proposes 

 to discuss the phenomenon briefly in its bearing upon reproduction 

 and the segmentation of the ovum, and also to pay some attention to 

 points of theoretical interest in the same connection. Before doing 

 so, however, it will be advisable to consider that other form of 

 nuclear division, viz., Amitosis, or direct division, to which 

 reference was made at the conclusion of the former article. This 

 course is almost necessitated by the fact that recent observations 

 tend to show that amitosis sometimes occurs where theoretical 

 considerations would naturally lead one to expect karyokinesis. If 

 tlie accuracy of these observations be allowed, it would seem that 

 nuich that has been written on the significance of karyokinetic 

 division in the transmission of hereditary substance must be recon- 

 sidered, if not laid aside as no longer compatible with attested facts. 



Amitosis, and its Relation to Mitosis or Karyokinesis. 



Amitosis has been stated by many observers to occur normally 

 both in unicellular organisms and in the tissues of higher animals 

 and plants. 



Firstly, as regards its occurrence in the Protozoa. The student 

 of nuclear division in these animals must draw a sharp line of 

 demarcation between those forms which possess both a macro- and 

 micro-nucleus, e.g., Paramcecinin, and those which, like the common 

 amoeba, possess only one. In the former instances, the macro-nucleus 

 invariably divides amitotically. Can the same be said of the single 

 nucleus of the latter ? Flemming, Ziegler (i8), and those who seek to 

 show that amitotic division is invariably a sign of the degeneration 

 of the nucleus that exhibits it, maintain that in those forms which 

 have only one nucleus the division is always accompanied by 

 karyokinesis. Hence, if it can be proved undoubtedly that amitotic 

 division may take place in such forms as Amoeba, it follows that the 

 view of those authors must be disregarded, at any rate in so far as 



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