ALAJUELA AND THE VOLCANO POA'S 335 



in Peridromia fornax, however, even with Hampson's figure 

 before me. 



Going upstream, the Ciruelas River led chiefly through a 

 series of small, narrow, grassy potreros, each running to the 

 river bank and each one representing a different ownership. 

 About three-quarters of a mile upstream was a log bridge 

 (frequently swept away by the trees and other debris brought 

 down by the floods of the rainy season) which led into a 

 large potrero where the land rose into a considerable hill. 

 This formed the divide between the Ciruelas and Brazil 

 Rivers, the latter being much the smaller. At a point 

 roughly opposite the log bridge, the Brazil flowed through a 

 little ravine so thickly set with trees that it was exceedingly 

 dark. A few species of shade-loving dragonflies were found 

 here. Those which fly about in the bright sunshine of open 

 fields, pastures or ponds, or in brightly lighted open places 

 in the woods, are rarely found in the dark parts of the woods, 

 and vice versa. Along the same stream, flowing now 

 through dark woods, then open fields, then dark woods 

 again, even the same genus will be represented by one spe- 

 cies in the brightly-lighted, and by another in the dark, 

 parts of the stream's course. For example, near Alajuela 

 in the genus Hetcsrina, the bright-light species was cruentata, 

 the dark woods species capitalis. As Costa Rica, like many 

 other parts of Central America, was more densely forested 

 formerly than now, it is reasonable to suppose that the 

 cutting down of the trees has brought about a marked in- 

 crease in the abundance of cruentata and a corresponding 

 decrease in capitalis. Somewhat different results were ob- 

 tained near Cartago, where the elevation is fifteen hundred 

 feet greater. Here the sun-loving cruentata was common 

 along all the streams flowing down from Irazu, wherever these 

 were open and sunny, but in well-shaded places no Hetcerina 

 could be found. On the other hand, when I was at the Rio 



