Occasional Papers of the Museum of Zoology 7 



dwelling than any species we have in the north temperate 

 region. But the larger number of stream-frequenting dragon- 

 flies of both the tropical and the temperate regions are equally 

 attracted by ripples. It may be the sun shines more continu- 

 ously there than on the pools, that food is more plentiful, that 

 luxuriant aquatic growths furnish convenient perches and the 

 leaves and stems suitable receptacles for dragonfly eggs, and 

 that oviposition directly in the water by other species is safer. 

 At any rate, about the ripples of the larger northern stream 

 Hetaerinas, Enallagmas and gomphines congregate at their 

 season, while the ripples of some tiny brook in the tropical 

 jungle flashes with the brilliant blues of Argias and Coras and 

 the red of Hetaerinas. 



Tropical streams of about the same size as those in the 

 north where Hetaerinas may occur, streams thirty feet wide 

 or larger, have few, if any, Hetaerina inhabitants. In fact, 

 odonate life generally is rare on these larger tropical streams. 

 A few species find them congenial, and some others find suit- 

 able homes adjacent to the river in little habitats such as pools 

 at the face of a cHff, a log jam, or a bit of old river bed, but 

 not parts of the river habitat itself. These larger tropical 

 streams rarely attract Hetaerinas. 



The small streams where the bulk of Hetaerina life in the 

 tropics is found are probably in most cases more recent than 

 the species of Hetaerina which frequent them. If this is true, 

 such streams received their Hetaerina faunas by migration. 

 As to how this has come about, as stated before, we know as 

 little as we do about the origin of the species themselves. 

 Certainly, the species are not or have not always been as 

 bound to their restricted habitats as our observations would 

 indicate. 



