727 



ligenee. A result which stroiigljM'eniinds of the absence of sjstematiral 

 order in the "relative brain weights". 



1 have, therefore, treated the densities in a similar way as llie 

 brain weights, namely by considering them in connection with the 

 weights of the body. For this purpose calculating the mean densities 

 of the whole cortex (over those ten important tields), from Mayer's 

 records, I find a meaiT density of cell of 1765,4 for the Chimpanzee 

 (Anthropropithecus troglodytes), of 3160 for the Gibbon (Hylobates 

 syndactylus), of 3580.9 for the Capucliin-Monkey (Cebus capucinus), 

 of 3603.4 for the Saimiri or Squirrel-Monkey (Chrysothrix sciurea), 

 and of 3448.1 for the Marmoset (Hapale iacchus), which mean values 

 no more show systematic order than the densities in the separate 

 lie Ids, from which they are computed. 



This disorder is replaced by regularity, as soon as the size of the 

 animals is taken into account. 



The ratio ot the density of cells between the Chimpanzee and the 

 Siamang is as 1:1.79. The Chimpanzee has 8 times the weight of 

 this Gibbon-species, and now it is very remarkable that, between 

 these homoneuric species, according to the proportionality demon- 

 strated in my former paper, homologous cells must be more voluminous 

 to a ratio of 8"-28 = 1.79 foi' the Chim{)anzee than for this Gibbon. 

 Between these homoneuric species the density of cells is, therefore, 

 accurately in inverse ratio with the volume of every cell. In other 

 words: for a Gibbon that had the size of a Chimpanzee, the density 

 of cells in the cortex of the cerebrum would be equal to (hat of 

 the Chimpanzee. It may, therefore, be assumed that these xAnthropoids 

 of equal cephalisation (equal quantity of the brain in function of 

 the body weight) are also equal in the organisation of their cortex 

 of the brain. The cells of these two species must be uniform, both 

 as far as the dendrites and the other interstitium is concerned, and 

 with regard to the cell -body. 



When Cebus is conq)ared with Hapale, which he exceeds 6 times 

 in body weight (these weights are on an average 1300 and 215 

 grams; the brain weight of Cebus is 125, that of Hapale is about 8 grams), 

 the cortical density of cells for Cebus is found 1.7 times greater 

 than for a Hapale of equal body weight. In about the same ratio, 

 viz. 1.8:1 the cephalisation is, however, also greater for Cebus than 

 for Hapale, a very fair agreement when it is borne in mind that 

 different specimens were compared. Compared with (Jhrysothiix 

 (Saimiri), (whose body weight amounts to about 400 grams, and 

 which possesses 24 grams of brain) Cebus has 1.5 times higher 

 cephalisation, and a Saimiri of equal body weight as Cebus would 



