light prevcailiiig in the water (hat makes other senses than the optical 

 one predominate in these Manuiials, as likewise in the Fishes, and 

 probably in the Crocodiles (hearing very quick), in comparison with 

 Amphibia and most Reptiles. In the Fishes also the olfactory organ 

 and especially the sense-lines are predominant. This has caused 

 augmentation of the quantity of brain, because the surfaces of the 

 mentioned predominating organs of sense (in opposition to the eye, 

 which forms defnute images) increase simply proportional to the super- 

 ficial dimension of the animal (consequently with the exponent of 

 correlation 0.66. . .). So in these animals a vei-y considerable 

 increase of the quantity of brain does not signify a high degree 

 of organisalion. Calculated by means of the exponent of correlation 

 0.66...) /• becomes for Whalebone-Whales 0.07. for Toothed Whales 

 0.20 and for Seals 0.18. 



In the Snakes and the Slow Worm and likewise in the Eels, on 

 the contrary, the great length of the body is the cause of the low 

 value of k, though this does not therefore indicate an inferior degree 

 of organisation. In proportion to the weight of the body the not 

 specialised segmental sensu-motorical unities are too equivalent for 

 a representation in the brain, proportional to that of other Reptiles 

 and Fishes. The body becomes thereby, as it were, to a certain 

 amount, a ballast for the brain. This is in a more literal sense the 

 case in the Tortoises. In the shell-bearing Vertebrates and also in the 

 elongated animals the influence of the factor S^-^^ in the analysis i^ 

 has thus diminished. In the Eels a second cause of diminution of the 

 quaniity of brain exists moreover, in their life as animals of darkness, 

 by the disappearance for the greater part of the eye-factor >S^--^ in 

 (he analysis B and at the same time of the eye-factor in the analysis 

 .4 (as in the Bats). On account of the latter circumstance their r 

 becomes :r= 0.66. 



The influence of the not segmentally constituted eye in itself 

 remains in all cases restricted, from the nature of the factor S^-^'^ 

 which depends on it, and is thus less capable of increase. Even the 

 Horse, which possesses an absolutely larger (day-) eye than the 

 Elephant, rises still little above the average level of k for Mammals. 

 On the other hand can the other factor .S*'33, the segmental factor 

 in analysis B, grow, as it were, endlessly with the development of 

 "specific sense-energies" in the different segments. The tactile organs 

 have therefore always the lead with the higher organisation of the 

 nervous system. 25 November 1913. 



