1907.] Observations on the Life-history of Leucocytes. 501 



ancestor. This phylogenetic reversion of certain cells produced by the soma 

 may have become constant, and new characters may have been developed 

 from this fresh point of departure. This would account for the phenomena 

 exhibited by the leucocytes in the vertebrates. It has been considered 

 probable that spermatozoa are also examples of phylogenetic reversion to the 

 characters of protozoan ancestors. 



The possible conclusions to be derived from these observations may be 

 briefly stated as follows : Certain cells, probably only existing in the bone- 

 marrow in the case of the adult mammal, give rise to a group of cells which 

 are, or will immediately pass, out of somatic co-ordination. Some of these 

 are destined to comparatively rapid disintegration, probably including the 

 nutrition of other cells among their functions. Others pass through the 

 Meiotic Phase, and continue to divide, producing an apparently unlimited 

 number of post-meiotic generations of cells possessing half the somatic 

 number of chromosomes. The great majority of these are converted into 

 red corpuscles, serving a nutritive purpose. The remainder are fertilised in 

 the manner described in the observations here recorded, and, as is the case in 

 many unicellular animals, after fertilisation divide a number of times, thus 

 producing fresh generations of leucocytes, which may or may not sub- 

 sequently pass through the Meiotic Phase again. 



This would naturally lead to the further conclusion that the leucocytes 

 passing out of co-ordination with the soma live as parasites upon the parent 

 organism, and in themselves possess a complete life cycle. 



These observations would appear to have some bearing upon what has been described 

 as occurring in malignant growths. It has been stated that during the early stages of 

 malignant growths, leucocytes, entering into the cytoplasm of some of the tissue cells, 

 proceed to divide mitotically, synchronously with the nucleus of the cell that they have 

 invaded, the chromosomes of the leucocyte and the tissue cell becoming mixed and being 

 distributed between the daughter nuclei resulting from the mitosis.* This bastard form 

 of fertilisation seems to suggest some properties in the leucocytes different to those 

 possessed by any other cells in the body, excepting perhaps the sexual cells. This 

 suggestion is strengthened by the observations here recorded. 



A fusion between the cells of certain graftable tumours in mice has been described. t 

 These tumours were said to be malignant, though some doubt has since been thrown upon 

 this statement. A re-examination of the figures illustrating this alleged fusion of cancer 

 cells of mice suggests very strongly that some of them may be fusions of leucocytes such 



* Farmer, Moore, and Walker, " On the Behaviour of Leucocytes in Malignant 

 Growths," 'Trans. Path. Soc. London/ vol. 56, Part III, 1905. Ibid., "On the Cytology 

 of Malignant Growths," ' Eoy. Soc. Proc.,' B, vol. 77, 1906. Moore and Walker, 'First 

 Report on the Cytological Investigation of Cancer,' University of Liverpool, Cancer 

 Research Laboratories, ] 906. 



t Bashford and Murray, 'Roy. Soc. Proc.,' 1904. 



