107 



cropus major it is as 1 to 800, the comparison being made on the 

 body of a large old male. The difference between the large and 

 small species of Kangaroo depends on the brain not increasing in 

 proportion to the increase in the bulk of the entire animal. The 

 smaller species in any natural family of Mammalia, resemble the 

 foetus of the larger species in the greater proportional size of both 

 the brain and the eyes. 



2. On the Monkeys of the Amazon. 

 By Alfred R. Wallace. 



The great valley of the Amazon is rich in species of Monkeys, and 

 during my residence there I had many opportunities of becoming 

 acquainted with their habits and distribution. The few observations 

 I have to make will apply principally to the latter particular. I have 

 myself seen twenty- one species ; seven with prehensile and fourteen 

 with non-prehensile tails, as shown in the following Hst : — 



3 Howlers, viz. — Mycetes ursinus, M. caraya 1 and M. Beelzebub ; 

 1 Spider Monkey, — Ateles paniscus ; 



1 Big-bellied 'Mon\ej{Barrigudo of theBrazilians), — Lagothrix Hum- 



boldtii ; 



2 Sapajou, — Cebus gracilis (Spix) and C. apella 1 ; 



4 Short-tailed Monkeys, — Brachyi(rus couxiu, B. ouakari (Spix), 



B. riibicundics {fCalvus, B. M.), and a new species ; 



2 Sloth Monkeys, — Pithecia irrorata and an undescribed species; 



3 Squirrel Monkeys, — Callithrix sciureus, C. personatus and C. tor- 



quatus ; 



2 Nocturnal Monkeys, — Nyctipithecus trivirgatus and N. felinus ; 



and 



3 Marmoset Monkeys, — Jacchus bicolor, J. tamarin and a new spe- 



cies. 



The Ilowhng Monkeys are generally abundant ; the different spe- 

 cies, however, are found in separate localities ; Mycetes Beelzebub 

 being apparently conhned to the Lower Amazon, in the vicinity of 

 Para ; a black species, M. carayal, to the Upper Amazon ; and a red 

 species, M. ursinus, to the Rio Negro and Upper Amazon. Much 

 confusion seems to exist with regard to the species of Howlers, owing 

 to the difference of colour in the sexes of some species. The red and 

 the black species of the Amazon, however, are of the same colour in 

 both sexes. The species of this genus are seminocturnal in their 

 habits, uttering their cries late in the evening and before sunrise, and 

 also on the approach of rain. Humboldt observes, that the tremen- 

 dous noise they make can only be accounted for by the great num- 

 bers of individuals that unite in its production. My own observa- 

 tions, and the unanimous testimony of the Indians, prove this not to 

 be the case. One hidividual only makes the howling, which is cer- 

 tainly of a remarkable depth and volume and curiously modulated ; 

 but on closely remarking the suddenness with which it ceases and 



