714 



(Jomparing- the gigantic Balaeiioptem |)liysaliis, whicli is likewise 

 somewhat sleiidei-er than Phocaeiia communis, with the latter, of still 

 more distant relationship, but which it exceeds 5323 times in weight 

 calculated according to the length, we find i\ = 0.2610 for a ratio 

 of the retinal areas of 1J500 : 1225 square millimeters. This value, 

 too, would certainly become somewhat larger, if the real weight 

 could have been taken into account, instead of what has been found 

 fiom the length. 



The deviations of the found exponeids of the value 0.277. . are not 

 very important if it is considered that -. 



1. The compared species are not all perfectly homoneuric, . 



2. also the specimens are not always typical for their species, 



3. the retinal area can oidy be calculated from the diameter of 

 the eye (in one case the weight of the eye) in approximation, 



4. in other cases the body weight was not directly determined. 

 In virtue of these and many other data, considered in the light 



of their physiological significance, I think 1 may assume that the 

 area of the retina really varies on an average proportionally to 

 /^.iK or more accurately /■'o.stt f^j. Ijomoneuric species of Vertebrates, 

 and that the same proportionality is of general application for the 

 area of the section of the homologous iiei-ve libers. 



About these relations for individuals within a species hardly any 

 direct data are available. IjAPicquk ^) states that for Canis familiaris 

 the diameter of the eye oidy varies from 20 to 23 mm., whereas 

 the body weight varies from 5 to 40 kilograms, i.e. about as the 

 fifteenth power root of this weight. For i\ we find here 0.1344, 

 which means the individual ocidar exponent of relation has de- 

 creased in the same ratio (taking the degree of accuracy of these 

 measurements into account), with respect to what is observed between 

 different species, as the ence|)halic exponent of relation. That the 

 found value lies nearer half 0.28 than half 0.22 may be remarked 

 in passing. 



Measurements of the thickness of homologous nerve fibers in 

 individuals of different weight of one species, to form an opinion of 

 the ratio considered here, are entirely wanting, but I think I may 

 deem it probable that the area of the section of the peripheral nerve fibers 

 remains the same, and that on the other hand the white nerve fibers 

 of the brain vary both in length and in section |M"oportionally to 

 po.u (-Q,. po.ii'^^^ which is in connection with the absence of the 



^) L. Lapicque. La grandeur relative de I'oeil et l'appréciation du poids encé- 

 phalique. Comptes rendus des seances de TAcadémie des Sciences. Paris 1908 (2). 

 Tome U7, p. '210. 



