270 THE WONDER OF LIFE 



so that plants and animals began to be afiected through 

 an ever-widening circle. 



Mr. Thomas Barb our has followed up the chain of con- 

 sequences as regards reptiles : 



' The introduction of the mongoose has caused the almost 

 complete extinction of many species which were once 

 abundant, and has in some ways radically changed the 

 facies of the fauna. In the back country, lizards are rarely 

 met with, and it is only in the vicinities of villages and 

 towns, where they are more or less protected, that one 

 may obtain satisfactory series of many species. The 

 true ground-inhabiting forms have, of course, suffered 

 most, so that lizards of the genera Ameiva, Mabuia and 

 Celestus are now scarce and difficult to obtain. Snakes 

 have suffered perhaps more than lizards.' 



An additional linkage in the case of the sparrow intro- 

 duced into the United States has recently come to light, 

 but it requires further investigation. The swarms of 

 sparrows drive away other birds, but they also appear to 

 exert an inimical influence on poultry in the wide sense 

 (fowls, turkeys, ducks, geese, etc.). In the sparrow's 

 intestine there are parasitic Protozoa, known as Coccidia, 

 which occur in great abundance. The sparrow is accus- 

 tomed to them, but when they pass to new hosts, such as 

 poultry, they cause serious diseases, known as ' blackhead ' 

 or coccidiosis. The parasites also occur in the American 

 ' robin ' (Merula migraloria), the quail, and the Ruffed 

 Grouse ; and perhaps there is a risk of making the sparrow 

 a scapegoat. 



The Living Earth. As an instance of subtle inter- 

 relations, we may refer to some recent investigations at the 

 Rothamsted laboratory. Drs. Russell and Hutchinson 



