1031 



days old he found (counting in mm») 46 mitoses in the cervical, 

 75 in the thoracic aud 14 in the lumbar region, but that in an 

 animal twenty days old he could not show a single one. 



Hamilton^) found in thirteen succeeding sections, 6,75 /t thick, 

 from the medulla spinalis of a four days old rat mitoses in the 

 ependyma and 64 situated extraventricularly. 



Addison W. H. F. ') found in au "albino lal" nearly 22 days old 

 mitoses "in the other granule layer" of the cerebellum. 



ScLAVUNOS G. ') has obseived mitoses in the central nerve system 

 of new-born dogs. 



SuGiTA Naokf ''), who has studied the post-embryonic growth of 

 the cortex of the brain in the "albino rat", found that the value 

 for the number of cells in this region in the ten days old animal 

 was 1,9 X the value at birth, and that the number of cells increases 

 further dui-ing the next ten days and is complete at twenty davs. 

 After this time the number of cells is practically constant and the 

 number of cells in the fuUy-gi-own state is approximately twice as 

 great as at birth. These calculations are based on the determination 

 of the number of cells in only two layers at only one place and 

 therefore their general value may be questioned. S. has, however, 

 previously shown by measurements made at different places on the 

 cortex of the brain that it undei'goes the same relative increase in 

 thickness between birth and maturity. S. considers that the values 

 obtained may therefore with great probability be generalized foi- the 

 whole cortex. With regard to the way in which such a post-em- 

 bryonic increase in the number of cells in the coilex takes place 

 one can, of course, herein supported by Allen, who in 25 days 

 old specimens of the "Albino rat" found as many as 27 mitoses 

 per mm' of tissue in the cerebrum, consider that it is due to 

 mitotic division. 



The values given for the number of mitoses and for the increase 

 in number of the cells in the central nervous system do not refer 

 to any definite number of cells, but apply to all the cells taken 

 together, and thus do not exclude an increase in the number of 



^) Hamilton. Alice, The division of difTerenlial cells hi the cenfral neivous 

 system of the white rat. J. Gomp. Neui., Vol. II, pp. 297—320, 1901. 



-) Addison, W. H. F., The development of the Pnrkhije cells and of the cortical 

 layers in the cerebellum of the Albino ?'«^. J. Gomp. Neurol. Vol. 21, pp. 459— 487. 



') ScLAVUNOS, G., lleber Keimzellen in der weissen Subslanz des Rückeumarks 

 von alteren Embryonen und Neugeborenen Anat. Anz., Bd. 16, 1899. 



*) SuGiTA Naoki, Gomparative Studies on the growth of the Cerebral cortex 

 III, IV and VI, Journ. Comp. Neur. Vol. 29, 1918. 



67 



Proceedings Royal Acad. Amsterdam. Vol. XXI. 



