132 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY 
Conclusions 
It is clearly evident that the problem of distribution has two 
distinct aspects. First, that every species has a given interrelated 
latitudinal and altitudinal range; and secondly, that within this 
range species are to be found only at certain environmentally ac- 
ceptable stations. Ranges are geographical, stations ecological 
To determine a species' distributional status, whether northern or 
southern, by its range alone, gives an inadequate impression. 
Only an ecological study of the station formation at which it is 
found can determine its proper classification. The ecological 
characteristics of Odonata species are at present little understood, 
and any definite placing of species is entirely provisional depending 
on further investigation. Species, of course, do not inhabit all 
acceptable ecological stations (the places vides of recent French 
investigators), within their range, any more than a certain oak- 
loving species can be expected to be found on all such trees within 
a forest or within its range. Species, in other words, are not spread 
out evenly over the entire area occupied by them. A species, 
therefore, it is plain, may inhabit one or more, often three, zones 
and even two regions, as defined by Merriam, and still belong to 
only one type of ecological station. In fact it is comparatively rare 
to find a species so elastic in its environmental requirement that 
it can inhabit more than one such (ovipositing) station. When a 
species is common to two types of ecological station they are at 
opposite latitudinal limits of their range, or, a normal range sta- 
tion and an extra-limital one. 
To attempt to define therefore too closely and arbitrarily zone 
boundaries in verbal terms, e.g., Upper Austral, is to confuse rather 
than to elucidate the problem. Only when a given species' distri- 
bution can be stated in both geographical and ecological terms, e.g., 
''Agrion amatum, Lat. 35.15° (3000 ft.) to Lat. 45.3^ (sea level), 
Long. 71° to 83° W., rapid, rocky, woodland streams" — can any 
degree of accuracy of expression be attained. Intensive collecting 
will then, frequently in a moment, and readjustments of Nature, 
over long periods of time, extend or vary the known geographical 
ranges. Far less often will Nature through survival necessity alter 
the ecological requirements. The latter it is clear become there- 
