440 MEMOIRS OF THE CARNEGIE MUSEUM 
toward the head-waters of these rivers and to closely approach the divide toward 
Lake Erie.* 
This would favor a direct crossing of the divide by actual migration over land, 
and indeed the river-species are able to survive when out of the water for a consid- 
erable time under certain circumstances, as I have ascertained by experiments. 
During hot and dry weather it is hardly possible to keep them alive for more than 
an hour or two; but in cool, cloudy, and damp weather I have found that speci- 
mens suspended on a string on an open veranda” were not dead after seven hours, 
and restored to water, recovered entirely. This might at least render a 
migration over land possible, but I do not think that it actually takes place, 
since it has never been observed, either by othérs or by myself, that ©. ob- 
scurus, or any other species classed ecologically with the river-species, leaves 
the water voluntarily. On the other hand it is possible that C. obscurus may 
undergo a passive transport from one drainage to the other, as for instance by birds. 
However, I do not believe that the crossing of the divide toward Lake Erie is due 
to the latter cause. It seems to me highly improbable, not that birds should be 
able to carry crawfishes for a long distance, but that it should happen that a bird 
should take up a crawfish in one stream, carrying it to another safe and sound, and 
drop it there without hurting it. Birds do take crawfishes” and sometimes carry 
them short distances, but this always results in serious injury, even if the specimen 
is not immediately eaten. Thus, even though we may admit that crawfishes might 
be transported by birds without being injured, such cases must necessarily be 
extremely rare, and do not happen often enough to effect the establishment of a 
species in a drainage system from which it was originally absent. 
There are other considerations which make the assumption of passive transfer 
improbable in our case. Toward the east C. obscuwrus is (with exceptions to be dis- 
cussed below) rigidly restricted to the Ohio drainage, and nowhere crosses into that 
4 At Linesville, Crawford County, I found this species in the very headwaters, almost in the springs running into 
Shenango River just south of Summit, which is on the divide. 
55 Particulars of one of the experiments (I have made a series) are as follows: November 9, 1905. Cloudy day. 
Mean temperature: 34° F. Light breeze from West-South- West, and light snow in afternoon. Specimens of C. obscurus 
suspended on strings on veranda with southern exposure. Beginning of experiment 9a.m. Onespecimen taken in at 
2p. m., another taken in at 4p. m., and put into water. Both alive and vigorous next morning, and were kept alive 
till December 18, when they were thrown into alcohol. 
In midsummer, on hot days, I often observed that the vitality of C. obscurus becomes very low after they are only a 
short time out of water. They may die within an hour, without having been subject to any other injury than that 
caused by the removal from the water. 
5°Mr. W. E. C. Todd informs me that remnants of crawfish are quite usual in the nest of the kingfisher. I have 
seen, in the collection of the Department of Agriculture, Harrisburg, a specimen of C. burtoni, taken from the stomach of 
a kingfisher. 
