1903.] of Malignant Growths in Man. 501 



The essential features wherein this heterotype mitosis differs from 

 those of the body or soma of the organism (whether plant or animal), 

 as well as those in the cell-generations of the reproductive tissues that 

 have preceded it, are as follows : 



1. The period of rest and growth. 



2. The chromosomes where they are formed from the resting nucleus 

 are present in only half the number of those occurring in the rest of the 

 dividing nuclei of the organism. 



3. The forms exhibited by these chromosomes are strikingly different 

 from those of other nuclei. They produce figures resembling loops, 

 rings, aggregations of four heads, and so on. 



4. Their division on the spindle is transverse and not longitudinal. 

 It will be thus seen that this heterotype mitosis is an easily 



recognised phase in the history of the development of the sexual 

 cells, and for our purpose this is the essential point. With its 

 theoretical interpretation we are not here concerned. 



But it is a fact of the highest importance that when once the 

 heterotype division has supervened, all the descendants of that cell 

 retain the reduced number of chromosomes in normal cases. The 

 cycle \ of these cell-generations, the nuclei of which only forms half 

 the somatic number of chromosomes, normally closes with the forma- 

 tion of the definite sexual cells. It is on the fusion of two of these 

 (ovum and spermatozoon) that the double or somatic number is 

 restored, and this number is characteristic of the fertilised egg, and 

 of all the cells to which it gives rise, until the heterotype mitosis 

 again supervenes in the reproductive tissues. Now after the interven- 

 tion of the heterotype division, the cell in which it has occurred may, 

 after one further division, at once give birth to the four sexual cells, 

 as in the higher animals, or, on the other hand, a varying number of 

 cell-generations may be intercalated before the final differentiation 

 of the sexual elements. This occurs in the majority of plants. It is 

 in these latter that the commonly parasitic character of the organism 

 thus arising is specially, though not exclusively, apparent. Thus, the 

 embryo sac of many flowering plants exerts a destructive influence 

 on the cells of the soma adjacent to it. This property is not, however, 

 by any means exclusively confined to the post-heterotype formation 

 (the gametophyte of the plant), and we do not wish to lay distinctive 

 weight upon it. In the lower plants the bulk of the body is composed 

 of cells with reduced nuclei, and the alternate stage m the life cycle, 

 originating in the fertilised egg, is the predatory structure. What 

 seems to emerge from a general consideration of the whole range of 

 facts is this : that in the higher animals and plants the post-heterotype 

 tissue, with its own independence of organisation, does behave towards 

 the surrounding tissues of the parental individual as a neoplasm 

 So far as the parent is concerned, the new growth might be des< 



VOL. LXXII, 



