ZOOLOGY. 59 
numerous types of the southern North American Fauna are spread over Northern 
Mexico, extending along the Central American plateau to the extreme limits of our 
area, and even beyond. This southward extension of northern types is due partly 
to the identical physical conditions of the arid tableland of Sonora and Chihuahua, 
which is merely a continuation of that of Arizona and New Mexico, and partly to the 
great altitude and temperate climate of the Central American plateau. Thus, a 
boundary line between the North and South American regions cannot be drawn: 
Central America forms a transition-tract unlike any other part of the world, showing 
the most extraordinary diversity of climatic, physical, and meteoric conditions 
within comparatively small areas, favouring the evolution of a great variety of types 
of genera and species, and influencing the dispersal of immigrants from the North 
and South. 
The range of the 695 species enumerated is shown in the Table appended to the 
Introduction (pp. x—xvil). 
Since the conclusion of Dr. Giinther’s work, Dr. Hans Gadow has twice visited 
Mexico (1902 and 1904), mainly to study the distribution, &c., of the Amphibians and 
Reptiles. He collected specimens of 135 species. The following papers have been 
written by him :— 
(1) ‘Evolution of the Colour-pattern and Orthogenetic Variation in certain 
Mexican Species of Lizards, with Adaptation to their Surroundings ” [ Proc. 
Roy. Soc. Lond. Ixxii. pp. 109-125, pls. iii.—v. (1903) ]. 
(2) “The Mexican Axolotl” [‘ Nature,’ lxvii. pp. 330-332 (1903) ]. 
(3) “The Distribution of the Mexican Amphibians and Reptiles” [P. Z. S. 1905, 
ii. pp. 191-245]. 
(4) “ A Contribution to the Study of Evolution based upon the Mexican Species of 
Cnemidophorus” (P. Z. 8. 1906, i. pp. 277-375, pl. xx.). 
(5) ‘Through Southern Mexico.’ London, 1908. 
(6) ‘“‘ Geographical Distribution of Animals” [‘ Darwin and Modern Science,’ pp. 319- 
336 (1909). 
(7) “The Effect of Altitude upon the Distribution of Mexican Amphibians and 
Reptiles” [Jahrb. Jena Abt. f. Syst. xxix. 1910, pp. 689-714]. 
He also published an excellent account of the portions of Mexico visited during his 
travels, and we give elsewhere a copious extract from one of his papers. 
During recent years attention has been called to various Reptilia, Batrachians, 
Arachnids, Coleoptera, &c., living in the Bromeliads on the branches of trees. 
Specimens of Spelerpes variegatus and Hyla godmani were obtained from these plants 
by one of our collectors, Mateo Trujillo, in Mexico, and other species have since been 
captured by Dr. Gadow. 
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