ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 421 
usual time for working seems to be at night, and I have repeatedly observed that 
holes and chimneys disturbed or destroyed on one day exhibited signs of recent 
action on the following day. The crawfishes also seem to work occasionally on 
rainy or cloudy days; at all events, on such days it is easier to induce them to come 
to the mouth of the hole. 
As to the purpose of the “chimneys,” different opinions have been expressed. 
Abbott (1884) believes that the chimneys are designed, and that the crawfish intends 
to build just such structures, thatis to say, rather regular subconical mud towers. 
He maintains this against Tarr’s view (1884, p. 127), that the chimneys are not a 
necessary part of the burrows, and that they simply are the result of the digging. 
Subsequent writers have rather inclined towards Tarr’s idea, for instance Shufeldt 
(1896, p. 89), who says that it is easier for the crawfish to build a chimney than to 
carry the mud away from the hole, and that “it is the most convenient and safest 
way to get rid of the pellets, besides being the least troublesome, and the method by 
which they are the least likely to roll back into the burrow.” Harris (1903, p. 605) 
thinks that the chimneys very likely are only “the result of the easiest method of 
disposing of the material removed in excavating the burrow.” 
I must indorse the latter opinion, and for the following reasons. Regular chim- 
neys, although claimed by Harris (/. c.) to be “usually” present and well built, 
are by no means so frequent as believed by most authors. Of course they are 
abundant in each colony of chimney-builders, and attract the attention of the 
observer. However, according to my experience well built chimneys are rather 
scarce compared with the total number of holes existing in a particular locality. In 
the majority of cases only more or less irregular and shapeless mud-piles are found 
at the mouths of the holes, and it is only under certain favorable conditions that they 
assume the shape of “chimneys.” These conditions occur when the upper part of 
the hole is more or less vertical (see Pl. XL, Fig. 9 at A; Pl. XLI, Fig. 2 at C; Figs. 
7 and 8), so that there is opportunity for the crawfish, in bringing up the pellets of 
mud, to deposit them rather uniformly all around the rim of the chimney. Sup- 
posing that it is always the lowest part of the rim at which additional pellets are 
deposited, which is altogether a very likely supposition, if the crawfish wants to get 
rid of the pellets as quickly as possible, the chimney must grow regularly. If, how- 
ever, the mouth of the burrow opens in a slanting direction or horizontally, more or 
less one-sided mud-piles will be the result. (See Pl. XLI, Fig. 2 at A; Figs. 3 and 
4). Further, much depends on the character of the material brought up. If it is 
fresh clay (not disturbed before), as will generally be the case when the crawfish is 
digging out a new hole, the pellets will be firmer, stick better to the rim of the chim- 
