1907.] Observations on the Life-history of Leucocytes. 499 



This class of leucocytes, which is described in more detail elsewhere,* forms 

 a large proportion of the cells in the spleen and the majority of those in the 

 lymphatic glands. 



It is necessary, before considering the probability of fertilisation being a 

 correct interpretation, to dismiss the probability of the process being 

 simply the destruction of one cell by another. This is a very common 

 process, but seems always to take the form of engulphment of the whole or 

 part of the cell destined to destruction into the cytoplasm of another cell. 

 The usual sequence in the case of vertebrates is, that one leucocyte or other 

 kind of cell engulphs another bodily into its cytoplasm. The engulphed cell 

 is gradually disintegrated. The nucleus first shows signs of degeneration. 

 At a later stage the whole cell somewhat resembles an archoplasmic vesicle 

 or Plimmer's body, and eventually it disappears altogether, both nucleus and 

 cytoplasm. The engulphed cell is never taken into the nucleus, but remains 

 in the cytoplasm of the engulphing cell, and is there apparently digested. 

 This phenomenon may be seen taking place in many different tissues, 

 particularly where there is any disturbance from the normal condition. It is so 

 totally unlike what has been here described as taking place among the leucocytes 

 in Axolotl and mammalian spleen, that it is unnecessary to go into further 

 details.f The process of engulphment and destruction of one cell by another 

 is, in fact, morphologically a very simple and straightforward affair, and takes 

 place without the development of any special apparatus on the part of either. 

 On the other hand, the absorption of one leucocyte nucleus by another, as 

 here described, seems to involve the development of a special and complicated 

 apparatus, formed in such a manner that the chromatin and linin of one 

 nucleus may be transferred directly to the other, without any process of 

 digestion by the cytoplasm being possible. 



It might possibly be suggested that certain prolongations of the nucleus 

 and cytoplasm which are very common among the leucocytes found in the 

 mammalian spleen might be confounded with the figures here described. A 

 careful examination shows that they are of quite a different nature, and so 

 dissimilar as to be hardly comparable. 



The morphological evidence would therefore appear to be in favour of 

 fertilisation, in that the nuclear contents of two cells are apparently fused 

 without any disintegration of the contents of either nucleus taking place, 



* C. E. Walker, " On the Origin and Differentiation of the Red Blood Corpuscles of 

 Mammals," loc. cit. Ibid., " Observations on the Life-history of Leucocytes," loc. cit. 



t Figures illustrating the appearance of engulphed cells may be seen in the ' First 

 Report on the Cytological Investigation of Cancer,' Moore and Walker, 1906, Cancer 

 Research Laboratories, University of Liverpool. 



