249 



is found in (he establishment of a new homoneuric species — certain 

 parts of this organ increase to a greater degree than the otlier parts, 

 and accordingly a heteroneuiic species originates, is probably always 

 too accompanied with increase of the bulk of the body. Only with 

 the same increase of the bulk of the body, the increase of the 

 volume of the brain is comparatively greater than in the establishment 

 of a new homoneuric species. 



Another peculiarity of the Polecat may be considered in connection 

 with what has been said about its lower cephalisation. When 

 with the observations of weight of the body and the brain by 

 Bethcke*) of ten certainly adult polecats, the ontogenetic exponent 

 is calculated, from the five with body weights above 1000 gi-. 

 (average 1281.5 gr.) and the five under 1000 gr. (average 769 gr.), 

 0.42 is found for it, the same value as is obtained froaj the weights 

 of a very large polecat (of 1700 gr.), from the observations of 

 Lapicquk*), and a very small one (of 593 gr.), of my own obser- 

 vations'), both adult animals. This exponent is exactly halfway 

 between Vis and Vg- I" a graph the direction of the ontogenetic line 

 of the Polecat would be seen to deviate from other ontogenetic lines, 

 and appioach to coincidence with the phylogenetic line of (he genus 

 Putorius. Evidently the species of Polecat is in a state of disintegration. 

 Probably the other Putorius species are too. Well-known is. indeed, 

 the great variability of all the species of this genus. 



In the ontogenetic growth there is an important difference between 

 the nerve cells and the other cells of the body. It is the great 

 merit of Giuseppe Levf and of Edwin Conklin to have pointed this 

 out. In 1906 Levi*) proved for a great number of Mammalia and 

 in 1908 for the Vertebrates in general*), that in contrast with most 

 cells, except probably the muscle fibres (and those of the crystalline 

 lens), the size of the nerve cell increases with the size of the 

 animaP). The other cells increase in number, not sej)arately in size. 



1) Loc. cit., p. 613. 



') Gomptes rendus. Académie des Sciences. (2), Tome 151, p. 1393. Paris 1912. 



») Verhandeling of 1897, p. 36. Also: Bulletins de la Société d'Anthropologie 

 de Paris, 1897, p. 371. 



*) Loc. cit. 



5) Giuseppe Levi, I Ganglt cerebrospinal!. Supplementa al Vol. Vll dell' "Archivio 

 Italiano di Anatomia e di Embriologia". Firenze 19(18. 



^) Ikving Hardesty, already in 1902, found that the size of the motor nerve 

 cells from the spinal chord of various Mammals increases with the size of the 

 body. (Observations on the Medulla spinalis of the Elephant with some Comparative 

 Studies of the Intumescentia Gervicalis and the Neurones of the Columna Anterior. 

 Journal of Comparative Neurology. Vol. XII, p. 125 seq. Philadelphia 1902). 



