500 Mr. C. E. Walker. [May 15, 



and that the fused nuclear contents continue to exist in a common 

 cytoplasm. 



If we accept the interpretation that the apparent fusion of the nuclear 

 contents of two leucocytes is to be regarded as the fertilisation of the 

 one by the other, a remarkably complete, although complex series of 

 phenomena is suggested ; a series of phenomena which, however surprising 

 it may appear at first, is found on careful examination to be analogous in 

 many respects, even in detail, to several equally complicated series of 

 phenomena that have been generally acknowledged to occur. 



It is necessary here to describe briefly those phenomena in plants with 

 which it is proposed to compare those occurring among leucocytes. 



A certain group of cells belonging to the soma becomes differentiated and 

 passes out of somatic co-ordination. Some of these, the tapetal cells, without 

 passing through the Meiotic Phase, exhibit changes which render them 

 different in function to the cells of the soma. They are destined to 

 disintegration in a comparatively short time, quite independently of what 

 happens in the soma or among the rest of the cells of this differentiated group. 

 They serve a nutritive purpose. Other cells of the group pass through the 

 Meiotic Phase. Of these, only a few of the individuals produced by many 

 subsequent generations are destined to reach the stage where conjugation 

 may take place with other cells in the same condition. The rest produce 

 a comparatively unlimited number of post-meiotic generations, and carry 

 out the function of nourishing and supporting those cells destined to 

 conjugate. 



Apparently a number of the cells belonging to the early generations of 

 leucocytes do not pass through the Meiotic Phase, but though they are 

 apparently out of co-ordination with the soma, they serve nutritive and other 

 purposes, some among them developing granules.* 



Other leucocytes, apparently belonging to later generations, pass through 

 the Meiotic Phase. Of this group the greater number appear to be 

 converted into red corpuscles, thus serving a nutritive purpose.f Others of 

 this group, if the fusion of nuclear contents be regarded as fertilisation, 

 conjugate with other reduced cells. 



It may be that when, during the process of evolution, leucocytes or their 

 immediate precursors were developed and passed out of co-ordination with 

 the parent soma, these cells reverted to the characters of a remote protozoan 



* C. E. Walker, " Observations on the Life-history of Leucocytes, Part II," 

 supra. 



f C. E. Walker, "On the Origin and Differentiation of the Eed Blood Corpuscles in 

 Mammals," loc. cit. 



