664 



Lapicque has measured the diameters of the eyeballs of a number 

 of Vertebrates and found for Mammals an e:siponent of correlation 



first of — , afterwards of — ^). For the examined Mammals the 



8 ' ' 



measurement of the diameter of the ej'e-ball was generall}' sufficient in 

 order to ascertain the size of the retina. He concludes then, as was 

 to be expected from what could be shown already in 1897, that 

 in most cases the size of the eye runs parallel with the weight of 

 the brain. 



Those meritorious measurements of the eye-ball by IjAPICQUE thus 

 furnish a welcome affirmation of the results obtained here with regard 

 to the images on the retina. We may admit that the linear dimen- 



7.5 



sions of the images vary as \/ S or ^S'*^-'^^* • . 



9 1 



If the result had been |,/>Sor /S'*^'" •• ^ L^, then we should have 



here the same factor as in the coefficients for the brain, and we should 

 immediately be convinced of its rational character. Now it can, again, 

 not be by chance only that even in apparently absurd compari- 

 sons (as those of Sibbald's Fin-Whale with species of little land- 

 animals) that same exponent '/7.5 constantly returns. What is the meaning 

 of this fact? 



The answer to this question too is not difficult, for 9:7.5=: 

 0.66 . . : 0.55 ... If now we consider that, in accordance with the 

 augmentation of the brain with the size of the species of animal, the 

 sensitive surfaces must increase in the same proportion to the superficial 

 dimension of the body, then it becomes comprehensible that the receptive 

 sense-elements in the retina do not remain entirely equally thick 

 with the larger animal as with the smaller one, but become thicker 

 and less closely placed "), in the .same proportion. For this reason 

 the niunher of the nerve-elements in the retina increases only linearly 



1 2 



9 _L 9 Jl 



as VS or L^ , in the superficial dimension as V^ S- ^=^ S ^ oyS^-^^-- 



2 



In this way a connection has been established between the expo- 

 nent of correlation for the eye and the exponent of correlation for 



1) "La grandeur relative de Toeil et l'appréciation du poids encépbalique". Gomptes 

 rendus de FAcadémie des Sciences. Paris, Tome 147, (1908), 2, p. 209. "Relation du 

 poids encéphalique a la surface rétinienne dans quelques ordres de Mammifères". Ibid. 

 Tome 151, (1910), 2, p. 1393. On lower Vertebrates: L. Lapicque el H. Laugiea 

 in Gomptes rendus de la Société de Biologie. Tome 04, (1908), p. 1108. 



2) Gompare the data in A. Putter, Organologie des Auges. 2nd Ed. Leipzig 1912. 



