1895.] 



On the Granular Leucocytes. 



71 



as to where it can be placed short of the zero advocated by some 

 supporters of panmixia, involves either a mortality due to periodic 

 selection or a magnitude of the regression coefficient vastly greater 

 than any which are in the least supported by such statistics as have 

 hitherto been collected. 



(in.) Natural selection is more rapid in its effects when unaccom- 

 panied, than when accompanied, by that form of sexual selection 

 which has been termed assortative mating. 



V. " On the Granular Leucocytes." By G. LOVELL Gulland, 

 M.A., B.Sc, M.D., F.R.C.P.E. Communicated by J. N. 

 L angle Y, F.R.S. Received August 27, 1895. 



(Abstract.) 



Leucocytes whose finer structure is to be examined must be fixed 

 by reagents, of which the best is sublimate ; drying is unreliable, as 

 it does not preserve details of structure. 



Tt is impossible to divide leucocytes into a haemal variety and a 

 ccelomic variety, for (1) lymphocytes are the precursors of all forms ; 

 (2) leucocytes are not present in the blood in early foetal life ; (3) they 

 are constantly passing from blood to connective tissue and vice 

 versa; (4) the mitotic reproduction of leucocytes takes place almost 

 entirely in adenoid tissue. It is only their size which prevents the 

 largest hyaline, eosinophile, and basophile cells from appearing in 

 the blood. 



M. Heidenhain's observations on the relative positions of nucleus 

 and centrosoraes are correct, but his theory of the original equality of 

 the " organic radii" will not hold. These main threads of the mitoma 

 are connected at every microsome by subsidiary threads. The 

 nucleus does not lie free in the interfilar spaces, but its linin net- 

 work is connected with the cytomitoma, and the two are perhaps to 

 a certain extent interchangeable. This would explain the variety of 

 arrangement of the nuclear chromatin, and the co-ordination in 

 movement of the cell-body and nucleus. 



The shape of the nucleus has no relation to the presence or absence 

 of granules in the cell-body, but depends on (1) the relative sizes of 

 the cell-body and nucleus (according to M. Heidenhain's law) ; (2) the 

 position of the centrosomes ; (3) the condition of rest or movement 

 of the cell. 



All varieties of leucocytes are merely stages in the development of 

 a tissue. They may be divided for convenience, and with regard to 

 the presence or absence of granules, into three main groups, the 

 Hyaline, Acidophile, and Basophile. These forms are all derived 

 from the lymphocytes, which are the daughter-cells derived from the 



