1899.] DH. A. KEITH ON THE CHIMPANZEES. 309 



Darwin's point appears more frequently in the Gorilla than in the 

 Chimpanzee. It appears in 9 per cent. Chimpanzees and 26 per cent. 

 G-orillas, the last figure corresponding to its appearance in Man — 

 taldng an average of various races. The development of the ante- 

 helix in the Grorilla approaches that of Man more nearly than the 

 Chimpanzee. The muscles of the ear are more rudimentary in 

 the Gorilla than in the Chimpanzee. Almost in every point the 

 ear of the Gorilla is the more human of the two. The external 

 ear is certainly an aid in distinguishing between the Chimpanzee 

 and the Gorilla. 



8. The Circulatory and Digestive Systems of tJie 

 Gorilla and Chimpanzee. 



Our knowledge of these systems in the two African anthropoids 

 is founded on a too limited amount of material to allow of any 

 definite statement being made as to the points on which they 

 differ. On the whole, they appear to resemble each other very 

 closely. The only feature that appears to demarcate them is 

 seen in the liver. The right lobe of the Gorilla liver shows always 

 a deep fissure, separating oflf a right lateral lobe, a fissure which 

 occurs vary rarely in the Chimpanzee and only occasionally in the 

 Orang. The liver of the Gorilla, in its division, is the most 

 primitive form found in the Anthropoids and most nearly resem- 

 bles that of the lower Catarrhini. On the other hand, especially 

 in its bulbous glans penis, the genital system of the Gorilla is the 

 more human. Laryngenl sacs occur both in the Gorilla and 

 Chimpanzee, and it is rather strange that " Johanna " has never 

 been observed to manifest its presence. 



9. Hairs and Pigment as distinctive Features of the Gorilla 



and Chimpanzee. 



Neither the colour nor arrangement of hair, nor the degree to 

 which the skin is pigmented assist much in the differentiation of 

 the adult female Chimpanzee and Gorilla. In Antliropopiihecus nir/er 

 the pigment appears much later than in the other Chimpanzees, 

 and circum-oral and supra-orbital parts of the face appear never to 

 become deeply pigmented. The skin of the Gorilla, especially the 

 face, ears, palms, soles, and dorsal aspects of the trunk and limbs, 

 are deeply pigmented at birth. The adults of A. calvus and 

 A. hooloo-Jcamha show an equally intense deposit of pigment ; so 

 does the Central-African variety, but it is unlikely they are 

 so deeply pigmented at birth. The scalp of A. kooloo-kamba, 

 taking Johanna as an example, seems almost as thinly supplied 

 with hair as A. calvus. The arrangement of hair is the same 

 in all. 



10. Features of the Face and Skull tvhich are characteristic 



of the Chimpanzee. 



Next to the teeth, the most characteristic features of the Gorilla 

 are to be found in the structure of its nose. The Gorilla retains 

 Pboc. Zool. Soc— 1899, No. XXI. 21 



