1906.] Observations on the Life- History of Leucocytes. 55 



fig. 6). In fig. 11 a corresponding stage in the prophase of the first maiotic 

 division in the testis of a guinea-pig is given as a comparison.* Beyond this 

 again one occasionally finds a cell in the diaster stage in which some at any 

 rate of the chromosomes are longitudinally split (see fig. 17). This is typical 

 of the first maiotic division.f In so far as the leucocytes are concerned, 

 I have hitherto found this type of division only in the bone- marrow. 



The typically somatic division figures and those that I have interpreted as 

 heterotypes, however, even when taken together, are less numerous than 

 another form of division of which figs. 18 to 23 are illustrations. This form 

 of division is extremely common in bone-marrow and in lymphatic glands. 

 Hitherto I have not found it in any other adult tissue or in any other tissue 

 that I have examined, with one exception referred to later. 



It is obvious, as will be seen from the figures, which are taken from cells 

 occurring in the bone-marrow and lymphatic glands of the guinea-pig and 

 rat, that the number of chromosomes is not more than half the normal 

 somatic number, which is 32 in both cases. The shape of the chromosomes 

 seems to vary slightly in different cells. Some are short, thick, and slightly 

 curved rods (see figs. 18 and 22). Others are more or less oval, often very 

 irregular. There seems to be every reason for regarding these divisions as 

 similar to the second maiotic (homotype) division. F.xamples of this 

 division from the testis of the guinea-pig are given in figs. 24, 25 and 26. 

 The great frequency with which this division occurs suggests strongly that 

 there are several generations of cells showing the reduced number of 

 chromosomes. The fact that in many cells the chromosomes are rod-shaped 

 while in others they are roughly oval, led me at first to believe that there 

 might be a well-defined difference between the first and the succeeding 

 generations after the first maiotic division. An examination of the testes of 

 several animals, however, convinced me that the same difference might be 

 demonstrated among the homotypes there (see figs. 24 and 25). How far 

 this is to be regarded as a real difference or merely the result of a presenta- 

 tion of the cell to the eye or to faulty fixation in some cells is here beside 

 the point, as we know that in these particular animals there is no further 

 division after the second maiotic (homotype)4 



In comparing the foregoing observations with what occurs in the normal 

 production of sexual elements in animals and plants, some remarkable 



* Farmer and Moore, " On the Maiotic Phase (Reduction Divisions) in Animals and 

 Plants," ' Quart. J ourn. of. Mic. Science,' vol. 48, Part IV, February, 1905 ; Moore and 

 "Walker, " The Maiotic Process in Mammalia," ' Thompson- Yates Reports,' University of 

 Liverpool, 1906. 



t Farmer and Moore, Moore and Walker, loc. ext. 



\ Farmer and Moore, Moore and Walker, loc. ext. 



