712 



transmitted from the center outward, the motor nerve tibers chiefly. Thus 

 the volume of homologous neurones increases proportionally to po-se. 



Also for theVolume of homologous neurones in the brain (certainly 

 to be compared, if not morphologically, yet as functional units with 

 the peripheral neurones), the same proportionality may be assumed 

 as for the neurones with .peripheral nerve fibers, as a[)pears from 

 the equal relations of quantity holding for brain-weight. 



Direct data concerning the relative areas of the sections of 

 homologous nerve fibers, are, however, at our disposal only to a very 

 limited degree as yet. Most of them refer to the eye, more particu- 

 larly to nerve ends, where the retinal area maiks the total area of 

 the receptive terminations of a very important group of centripetally 

 conducting nerves. Many of these data have been furnished to us 

 by Lapicquk, in collaboration with Laugikr and Watkklot ') through 

 measurements of the diameter of the eye in a number of Mammals, 

 Birds, Reptiles, and Amphibians; from these we can derive the 

 relative size of the retina in approximation. Though at first (1908) 

 Lapicque, in virtue of these measurements, assumed that the diameters 

 of the eye vary pretty nearly proportionally to the power '/s of the 

 body weight, he later on (1910) considered as more accurate pro- 

 portionality the power \/j of the body weight. According to the 

 first estimation of Lapicque the retinal area would have to vary 

 about proportionally to P'/» or P^-^, on the other hand proportio- 

 nally to P'f^ or po'28.i7 according to his last estimation. The data 

 as such allow, indeed, oidy estimation of the general result. 



Some examples may suffice here, derived in the first place from 

 the tables of Lapicque and his collaborators. For the exponent of 

 relation in question, which I shall denote by i\ in the formula 



(;)■•="• 



and 



log — log o 

 log P — logp 



where P and /) denote the body weights, and and o the retinal 

 areas (more accurately here the areas of section of the eye-ball 

 proportional to these in approximation) I find the following values. 

 In comparison of the area of section of the eye, computed from 

 the diameter of the eye, of Equus caballus and Antelope (dorcas?) 

 0.2643, of Canis lupus and Canis vulpes 0.2668, of Felis pardusand 



1) These Proceedings Vol. XX. (1918), p. 1337, Note 1). 



