713 



Felis domestica 0.2390, of Mustela putorius and Mustela enniiiea 

 0.3004; as a mean of tliese three pair of Carnivores 0.2687. 



Of the Reptiles examined by Watkrlot the gigantic Lizard Vara- 

 nus niloticus, with a body weight of 7500 grams and a diameter 

 of the eye of 5.8 mm., compared with the small Gecko Hemidac- 

 tylns Brooki (3 indiv.), which weighs only 4.9 grams and has a 

 diameter of the eye of 4.25 mm. on an average, gives the value 

 0.2942 for r„. Comparing the same Varan or Monitor with a Green 

 Lizard, Lacerta viridis (examined by Lapicque) of a weight of 16.8 

 grams and a diameter of the eye of 5.8 mm., I find r, = 0,25J7. 

 The mean of these two values is 0.2730. 



Among Amphibians I mention (again examined by Lapicque) Rana 

 fusca with a body weight of 53.0 grams and a diameter of the eye 

 of 6.6 mm., and Hyla arborea, with a body weight of 4.8 grams 

 and a diameter of 4.6 mm. They give i\ = 0.3006. 



Two species of Fishes according to Welcker ^), Cyprinus carpio 

 and Gobio fluviatilis (2 indiv.), of resp. 1817.3 grams and 42.2 grams 

 body weight, and 1550 and 238 milligrams weight of the eye (from 

 which here the sectional area is calculated) give }\ = 0.3290. 



Records of retina! areas of some adult species of aquatic mam- 

 mals, accurately computed from direct measurements, of which some 

 differ very much in the size of their bodies, may be found in 

 Putter's extensive treatise '). 



The most homoneuric species, Phoca barbata and Phoca vitulina, 

 whose body lengths were in a ratio of 3 : J .75 to each other, had 

 retinal areas of 2543 and 1980 square millimeters. Assuming uni- 

 formity of these animals, we find, for a ratio of weight of only a 

 little more than 5 : 1, r. = 0.2972. 



Of two Toothed Whales, which are, indeed, not so closely akin, 

 but with much greater difference of weight, Hyperoodon rostratus 

 and Phocaena communis, the ratio of length was 6:1, and the areas 

 of the retina 5000 and 1225 square millimeters. Assuming again 

 uniformity, we find for the ratio of the body weights 216 : 1 and 

 then r^^ 0.2617. As however the body of Hyperoodon is somewhat 

 slenderer than Phocaena, the real ratio of weight must have been 

 somewhat smaller; the real value of /■, was, therefore, somewhat higher. 



1) H. Welcker — A. Brandt, Gewiclitswerthe der Körperorgane bei dem Menschen 

 und den Thieren. Archiv fur Anlhropologie, Bd. 28 (1902), p. 60. 



2) A. Putter, Die Augen der Wassersiiugetiere. Zoologisclie Jahrbiicher. Abtei- 

 lung fur Anatomie und Ontogenie der Tiere. Jena 1903. p. 167, 174, 198, 209, 

 239, 243, 272, 280. The calculations of the areas of the retinae, not immediately 

 comparable, were made by A. Lerch. 



