314 PROF. HUXLEY ON THE alectoromorphjE. [May 14, 



not difficult to show, from other considerations, that these are really 

 the most important divisions which can be established for the geo- 

 graphical distribution of both Birds and Mammals. 



Thus, in addition to the Alectoropodes, the following important 

 groups of Birds are either confined to the northern area, or are re- 

 presented elsewhere by not more than one or two species — 

 Pteroclido', Vultui-idtB, 



Otididce, Upupidce, 



Gruidce, Bucerotidce, 



while, in comparison with the southern area, it is very poor in 

 RatitcB, Psittacomorphce, 



Peristeromorphce, Capriinulgidce. 



With respect to Mammals, the northern area is almost coincident 

 with the distribution of the Insectivora, and it is the headquarters 

 of the Vngulata; Catarrhine Apes and Lemurs are confined to it ; 

 and it contains only two species of Marsupialia, and very few of 

 Edentata. Among the lower Vertebrata, Ganoid fishes are not 

 found outside this area. 



To the southern area, on the other hand, are restricted : — 



The RatitcE (except St rut Mo). 



The Tinamomorphce. 



The Cuthartidce. 



The majority of the Pigeons and Parrots, and all the most pecu- 

 liar types of both. 



The Trochilid<B and the Aptenodytidee, with few exceptions. 



Many annectent, or apparently isolated, forms of birds, such as 

 the Palamedeidce, Psophidce, DicholophidcB, HeteroDwrphcc. 



Among Mammals, the Marsupialia are as nearly confined to and 

 coextensive with it, as the Insectivora are in respect of the northern 

 area. The Platyrhine and Arctopithecine Monkeys and the Mono- 

 tremata are confined to it. It is the headquarters of the Edentata, 

 and is very poor in Vngulata — so as exactly to reverse the characters 

 of the northern area in these respects. 



In a well-known and very valuable essay on the Geographical 

 Distribution of Birds *, Dr. Sclater divides the surface of the globe 

 primarily into an eastern and a western area, which he terms re- 

 spectively Paleeogcea and Neogcea. However, if we take into con- 

 sideration not merely the minor differences on which the species 

 and genera of Birds and Mammals are often based, but weigh the 

 morphological value of groups, I think it becomes clear that the 

 Nearctic province is really far more closely allied with the Palaearctic 

 than with the Neotropical region, and that the inhabitants of the 

 Indian and the ^Ethiopian regions are much more nearly connected 

 with one another and with those of the Palaearctic region than they 

 are with those of Australia-^. 



And if the great frontier line is latitudinal rather than longitu- 



* Jouvn. Proc. Linn. Soc. Zool. vol. ii. p. ISO. 



t M. PuL'lieran has insisted very strorgly and, as I think, justly on the essential 

 unity of the fauiuc of Europe. Asia, and Africa. 



