1334 



The species compared for the calculation ^) gave the following 

 values for r: < 



1. 1. and 6. Homo sapiens and Mus musculus albinus 0.2747 



2. 2. „ 6. Elephas indicus and Mus musculus albinus 0.2788 

 J. 5. „ 6. Mus norvegicus albinus and Mus musculus albinus 0.2805 



4. 5a. „ 6a. Mus norvegicus albinus and Mus musculus (Pu) 0.2832 



5. 8. „ 7a. Felis leo and Felis domestical) (Be) 0.2804 



6. 9. „ 10. Canis familiaris and Canis familiaris (Spi) 0.2975 



Mean 0.2825 



On the whole G. Levi's data and those of H. Obkrsteiner are 

 not suitable for these calculations, because they either refer to cell- 

 bodies from different parts of the spinal cord or from ganglia spinalia of 

 different places, or rest in general on measurements that could not 

 jield accurate lesults. ') G. Levi does furnish particularly accurate data 

 as means of measurements of in each case 100 cells from the 4^'' and 

 from the 5"' gauglion spinale, both of a dog of a body weight of 

 23 kg. aud one of 3.75 kg., self-evideutly of differeut race and 

 probably also of different sexes (they may be considered of different 

 species at any rate as regards ratios of braiu quantity). For the 

 Purkinje cells of the common mouse Obkrsteiner gives the mean 

 cross dimension, just as Addison for the albino rat. 



The mean value of r found is now pretty accurately half the 

 exponent of relation 0,56 found for (he brain. In other words: 



The brain volume inrreases proportionally to the square of the 

 increasing volume of homologous nerve cell-bodies. 



The cell-body, the cell-centre of the neurone is now only part, 

 even a small part of the entire cell, for the processes, and especially 

 the neurite or nei\'e fiber, constitute by far most of the substance 

 of the neurone. Donaldson computed for certain neurones of the 

 spinal cord of man that the cyliuder axis alone has a 187 times 



') Between the horse and the mouse the exponent of relation is found to be 

 0,2387, on the other hand between the cat and the mouse 0,8931. The signifi- 

 cance of the deviations may be discussed in a subsequent communication. 



') Comparison of Felis domestica with the only about four times heavier Felis 

 pardalis, in which the mean diameters of the largest homologous giant cells of 

 Betz are 60 and 69 micra (B. Lewis, 1. c. p 53 and 58), leads to a less sharp 

 definition of the exponent. Starting from the stated ratio of the body weights 

 4: 1, we find 0,30:24, on the other hand 0,2830 for a ratio of weight of 4.4: 1. 



') Compare Obeksteiner, Bemerkungen zur Bedeutung der wechselnden Grosse 

 von Nervenzellen, p. 3. 



