118 
THIRTEENTH REPORT. 
inee region and the expedition of last year to the Charity Islands have 
all contributed valuable data that we would not have except for the 
Survey. 
The work of the Survey, thus far, has been and must, necessarily, con- 
tinue to be field work, directed with a special view to collecting data 
bearing on the various problems involved in the study of the distribu- 
tion of our fauna. Systematic and continuous field work can only be 
done under the direction of the Survey. And that must be primarily 
the work of the Survey. There is no difficulty in getting competent as- 
sistance in ‘‘working up” all the material that may be collected. The 
difficulty is in getting the requisite material. And this it should be the 
duty of the Survey to provide. 
Take the subject, in which I am specially interested, for example. 
We know that our unione fauna is made up of two distinct elements. 
One, essentially boreal in its character, came in from the north and east. 
The other from the south and west. Many of the species came from 
faunal areas that are now wholly separated from the St. Lawrence Basin, 
in which Michigan lies. The question as to how these species were able 
to effect a lodgment in our territory is one of great interest and of con- 
siderable scientific importance. But. before we can adequately under- 
take to consider that problem, it is absolutely essential that we should 
know the exact range in the different drainage areas of the state of the 
various species involved, and, if possible, the causes that in the past and 
now seem to limit their range. And it is in just these essential par- 
ticulars that our present knowledge is deficient. Thus, in the Upper 
Peninsula, the fauna of the Ste. Mary’s river and of Lake Superior is 
entirely boreal in its character. The fauna of the Menominee river, the 
dividing line between Michigan and Wisconsin, on the other hand is 
composed of the Mississippian species that here, apparently, reach their 
northern limit. Whether this is exactly correct or not, we do not know 
as the several rivers flowing into Lake Michigan between the Menominee 
and the Straits of Mackinac are wholly unexplored. We should like to 
know) what the faunas of these rivers are and, when the dividing line 
between these two faunal areas is definitely determined, to know what 
the environmental conditions are that fix that limit a’nd prevent these 
southern species from creeping around and obtaining a foothold in the 
Ste. Mary’s river. This is only one of several questions involved in the 
same inquiry. 
In the same way, in the Lower Peninsula, the Saginaw-Grand Valley 
is apparently the northern limit of the range of most of the southern 
fauna that fill the waters of the counties lying south of that valley. We 
should like to know whether this is true and, if it is the fact, then, 
why it is so. But, unfortunately, scarcely anything is known in regard 
to the fauna of the counties occupying the central part of the state north 
of the Saginaw-Grand Valley, and we are blocked in our attempts to 
find an adequate explanation for this, apparent, fact by the almost entire 
lack of the data that we should have to enable us to undertake the con- 
sideration of the problem with any assurance of satisfactory results. 
These are but samples of many similar problems that appeal to the 
student of faunisties. And it would seem eminently proper that, so far 
as it can, the Survey should, in the future, plan its work with reference 
to these broader questions that appeal to the philosophical naturalist. 
