No. 411. CAMBARUS IMMUNIS HAGEN. 18 
9 
many places which I have visited in all stages of drying up. 
Possibly birds may eat a few, but probably these are mostly 
water birds which could easily get the crawfish in the shallow 
water at any time. 
In early September, 1900, I visited a pond, which earlier in 
the season had many crawfish in it, and found there were many 
burrows around the edge and but few animals in the pond. 
Upon digging out one of these burrows, which had a chimney 
about four inches high and five inches in diameter at the base, 
I found a large first-form male and a somewhat smaller female. 
The burrow was about fifteen inches deep and about one and 
one-half inches in diameter; at the bottom it was expanded 
into a cistern-shaped chamber about three and one-half or four 
inches in diameter. It appeared that the burrow had been 
carefully sealed by the animals. Some time later I examined 
the pond when it was almost dry and found no crawfish, but 
plenty of chimneys in various stages of disintegration. At 
about the same time in another pond, which contained more 
water, the crawfish were abundant. About the middle of 
October, 1900, I examined the burrows of C. immunis around 
the first pond mentioned above. Some of the burrows had 
chimneys, others were simply open at the top; probably those 
which had no towers were old burrows whose chimneys had 
been disintegrated by the weather. The chimneys were of 
different forms, some being almost regular, while it was evi- 
dent that others were formed simply by the mud being thrown 
out of the burrow. Sometimes the mud appears to be just 
thrown out on one side, then, after a considerable amount of 
material has accumulated, the remainder is thrown out wherever 
convenient, forming an irregularly circular mound one to three 
inches high and six to nine inches across, or sometimes a long 
ridge with the shaft in the middle, the material here being 
thrown out in both directions. Sometimes the work is stopped 
before enough mud has been removed to make it inconvenient 
to throw it all to one side; thus forming a crescent-shaped 
pile. The highest chimneys noticed were about five inches 
high and three inches in diameter at the top. These were 
sometimes much inclined from the perpendicular. On the 
