202 
0?r THE aEOGRAPHICAL 
plains or close brakes, of which no species exists in New 
Holland, while those of Southern Africa depart from the 
typical species. The Tree- Serpents are more especially 
peculiar to equatorial countries ; but, as they inhabit vast 
forests, or -well wooded countries, they are not found in 
countries where those necessary conditions of their exist- 
ence are not met with. This is probably the reason why 
these serpents have not been observed in the greatest part 
of Nevf Holland, and that Southern Africa supports but 
a single species of this family, anomalous besides, and ap- 
proaching to the genus Coluber. The three genera which 
compose this family of tree-serpents, are found in both 
worlds ; but it is remarkable, that the Dipsas of America 
never arrives at that great size which is observed in most 
of the Indian species, and that the Dryiophis of both 
Americas form a true geographical division in this, that 
they have the dentary system and the muzzle less de- 
veloped, and that the pupil of the eye is orbicular. The 
fresh-water serpents which are comprehended in the two 
genera, Tropidonotus andHoMALOPSis, are found in abun- 
dance in countries rich in lakes, or watered by numerous 
rivers. Hence it is that these animals are common in 
Asia, in America, and even in Europe, that they are pro- 
bably not met with at all in New Holland, and that they 
are scarce in Africa ; for there exists but a single species 
of Tropidonotiis in the southern parts of that vast conti- 
nent, and even this species presents an organization 
wholly anomalous. The Homalopsis even, which are pre- 
eminently fresh-water snakes, and essentially aquatic, and 
which belong to warm countries, have not been observed 
in New Holland, nor in Africa, whilst they abound in both 
Americas ; they even replace, in South America, the Tro- 
pidonotus, which has not yet been discovered in that vast 
peninsula. The geographic distribution of the genus Boa 
presents us with several facts worthy of notice. They are 
also serpents peculiar to hot climates. The true Boas are 
only found in South America ; they are replaced in the 
old world by Pythons ; but we find in the Indies several 
serpents very analogous to the Boa, but of very small 
size, and of which there does not exist in the w^hole west- 
