1 6 Invertebrate. 



are white or colourless. Many large caves, like 

 those of Kentucky, Adelsberg c., have thus peculiar 

 blind faunae. 



Sometimes the presence of one animal prevents 

 the diffusion of others ; thus in Africa the tzetze fly 

 renders whole tracts uninhabitable by oxen and deer, 

 which are destroyed by its poisonous bites. 



The fauna of a limited area of a continent usually 

 exceeds that of an island of equal size in its number 

 of specific forms ; and the fauna of an island lying near 

 a continent resembles that of its neighbouring con- 

 tinent. Oceanic islands or those isolated by very 

 deep straits have often remarkable faunae of their own, 

 e.g., the Galapagos and New Zealand. 



Tropical species are, as a rule, more limited in 

 range tnan are those of temperate climates, and simpler 

 animals are usually more widely distributed than are 

 the more complex. 



Fresh-water inhabitants are the fewest specifically, 

 and as a rule are simpler in organisation than allied 

 forms inhabiting other media. The fourth sub-kingdom 

 has no fresh-water representatives ; the second has only 

 two, and the third only five species living in this 

 medium ; while the others are not very numerously 

 represented in fresh-water. 



The sea is the home of nine-tenths of the inver- 

 tebrates (if we exclude insects), and there are also 

 definite ranges of extension to be noticed in the 

 cases of marine species. The conditions limiting 

 specific life in the sea are depth, cunents, and tem- 

 perature. 



Terrestrial animals are the most specialised, and 



