458 WHEELER. 



rinae in the list, because the distribution of the species of Ponera, 

 Stigmatomma, Proceratium and Sysphincta, with the exception of 

 Ponera coarctaia subsp. ycnn!!iylvanica, is imperfectly known, and 

 because I have no new data for publication. The ants of the genera 

 Proceratium and Sysphincta are very rare and seem to belong to the 

 Upper and Lower Austral Zones, but they will probably be dis- 

 covered in the Western States. I have, in fact, seen a male specimen 

 which seems to belong to one of these genera, from California. 

 Ponera pennsylvanica is confined to the Eastern and Central States, 

 Ontario and Nova Scotia. The genus is represented in the Western 

 and Southern States by at least two closely allied species (P. trigona 

 var. opacior and P. opaciceps), whose precise distribution is still 

 unknown. 



The great importance of the ants in the study of geographical dis- 

 tribution has not been overlooked by students of this fascinating sub- 

 ject. These insects are, indeed, specially fitted for the mapping of 

 geographical areas, for several reasons. They are not, like many 

 other groups of insects, absolutely dependent on specific food-plants, 

 their colonies are stable and stationary entities, chained to the soil 

 or to certain general plant associations, and they are exceedingly 

 sensitive to climatic and other environmental influences as shown by 

 the extraordinary development of geographical races (subspecies) 

 and varieties in practically all the species of extensive range. A few 

 authors have attempted to minimize these peculiarities on the ground 

 that the marriage-flight of male and female ants must permit of a wide 

 dissemination of the species. It is true that many species of ants 

 have a very wide range, e. g. Formica fusca, which is circumpolar and 

 Camponotus maculatus which is cosmopolitan, but this is, in all proba- 

 bility, the result of great geologic age, and while we must admit that 

 the nuptial flight of the female ant is practically the only means of 

 rapidly disseminating the species, it is easy to exaggerate its impor- 

 tance. It is natural to suppose that small flying insects, like many 

 female ants, must be carried long distances by air-currents, and these 

 females, when fecundated, are, of course, so many potential colonies. 

 But such observations as can be made in the field do not support this 

 supposition. Most female ants are heavy-bodied and have feeble 

 powers of flight. Moreover, the time during which they can use 

 their wings, especially after fecundation, is limited to a few hours at 

 most. The wing muscles very soon begin to degenerate and compel 

 the insects to descend, abandon their organs of flight and become as 

 completely terrestrial as the workers. During marriage flights female 



