ORTMANN: THE CRAWFISHES OF THE STATE OF PENN.SYI.VAXIA 421 



usual tiinc for working seems to be at night, and 1 have repeatedly observed that 

 holes and chimneys disturbed or destroyed on one day exhibited signs of recent 

 action on the following day. 'i'lic ci-a\vfishes 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 •' chinuieys," different opinions have been expressed. 

 Abbott { 1 884) believes that the cliimneys are designed, and that the crawfisli intends 

 to build j\ist such struc-tures, that is to say, rather regular subconical mud towers. 

 He maintains this against Tarr's view (1884, p. 127), that the cliimneys 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 

 (1890, p. 80), who says that it is easier for tlie crawti.sh 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 i-emoved in excavating the burrow." 



I must indorse the latter opinicm, and for the following reasons. Regular chim- 

 neys, although claimed by Harris (/. r.) to be "usually" present and well Iniilt, 

 are l)y no means so frequent as believed by most authors. Of coui-se they are 

 abundant in each colony of chimney-builders, and attract the attention of the 

 observer. However, according to my experience well built chinmeys are rather 

 scarce compared with the total numl)er 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 Aivorable conditions that tliey 

 assume the .shape of "chimneys."" Tbe.se conditions occur when the upper part of 

 the hole is more or less vertical (see PI. .\ b. Fig. 9 at .1 ; IM. .\l.i, I'ig. 2 at C; Fig.s. 

 7 and 8), so that there is opportunity for the crawfish, in bringing uj. the pellets of 

 mud. to deposit tiiem rather uniforiidy all around the rim of tiie chinuiey. Sup- 

 posing that it is always the lowest part of the rim at which additional pellets are 

 dei)osite(l, which is altogether a very likely supposition, if the crawfish wants t«i 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 We tlie result. (See I'l. .\l.l, l"ig. 2 at .1 : Figs. :; and 

 4). iMiilher, iiincli (lepeiKJs 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 tlie chim- 



