56 



Mr. C. E. Walker. 



[Jan. 9, 



similarities become evident. Amitosis occurs as one of the earliest known 

 phenomena in the production of spermatozoa in some animals if not in all.* 

 The first maiotic is, in spermatogenesis, immediately preceded by the 

 ordinary somatic form of division. Then follows the second maiotic division, 

 retaining half the somatic number of chromosomes as in the first maiotic. 

 No further division has been recorded in the case of animals. Except as 

 regards the latter point, what happens among the cells of the bone-marrow 

 seems to be in many respects parallel to what happens in those of the testis, 

 for the myeloplaxes very possibly, probably as I believe, correspond to the 

 more or less syncytial condition of the cells sometimes observed in vertebrate 

 testes, both arising amitotically.f 



In plants, however, we find that though the series of complicated cell 

 phenomena that occur in the production of sexual elements are practically 

 identical to what occurs in animals, other cells than those destined to become 

 mature sexual cells are involved in the maiotic phase. Without going into 

 details that would here be out of place, it may be pointed out that in many 

 cases in plants but comparatively few of the cells that pass through the first 

 maiotic division, and thereafter show but half the somatic number of 

 chromosomes, ever become converted into sexual elements, and also that the 

 number of post-maiotic generations (those following the second maiotic or 

 homotype division) is often very great, even if they can be considered in 

 many cases as having any definite limit at all. 



If the observations recorded above be correct, it would seem that the life- 

 history of the leucocytes, in so far as I have been able to follow it, shows 

 some remarkable points of resemblance to the life-history of those reduced 

 cells in plants to which I have just referred. This comparison is carried 

 even further by what has been observed with regard to the origin and 

 history of the foot-cells of the testis^ All the observations recorded above 

 were made upon adult tissues, but in the course of seeking for the origin of 

 the foot-cells I examined the testes of very early embryos of the guinea-pig. 

 Here, long before the formation of the tubules, the cells that are destined to 

 become foot-cells are practically indistinguishable from certain of the stages 

 observed in the leucocytes found in the bone-marrow and lymphatic glands 

 of the adult animal. In these cells, besides the ordinary somatic division 



* Meves, 'Anat. Anz.,' 1891, No. 22; 1894, 'Arch. m. Anat.' ; Moore and Walker, 

 loc. cit. Observations contained in a paper, not yet published, by Miss Embleton. They 

 were carried out in the laboratories of the Cancer Research, University of Liverpool. 



t Moore and "Walker, loc. cit. 



X Walker and Embleton, " On the Origin and Life-history of the Sertoli or Foot-cells of 

 the Testis " (p. 50, supra). 



