422 MEMOIRS OF THE CARNEGIE MU8EUM 



ney, and will remain in position, thus favoring the construction of a "well-built" 

 chimney. On the other hand, when the mud is very soft, chiefly so when the craw- 

 fish is not digging new holes, but only cleaning out the old ones, the pellets are not 

 firm, and the more liquid mud will flow down the outside of the chimney and ren- 

 der it lower and l)roader and, consequently, less " well-built." This latter fact also 

 explains why young specimens often con.struet the neatest and most elaborate chim- 

 neys ( Al>bott). Young specimens, when they begin to work, bring out undisturbed, 

 firm, and sticky clay, and tlie pellets are more likely to remain where they are 

 placed on the rim of the chimney, which thus becomes very i-egular. Old speci- 

 mens, on the contrary, live in holes which are ^practically finished, and when they 

 work it is rather a process of " housecleaning " than of " housebuilding." The mud 

 removed is more li([uid and less stick}', and thus the chinnieN'S are shapeless and 

 irregular. 



Very often the ojDening of the chimne}' is found closed. Abbott believes that 

 the closing is merely the result of the accidental falling in of tlie rim. This may 

 indeed happen, but in other cases it is plain that the crawfish closes the aperture 

 intentionally, and (lirard (1852) regarded this as the completion of the work of 

 chimney-building. Sbufeldt and Harris likewise believe that the crawfish itself 

 seals up the burrow. This is my own opinion, and with Girard I think that the 

 sealing up is the final act characterizing the completion of the burrow. Sealed 

 burrows are very often found (see PI. XL, Fig. 9; PL XLI, Figs. 2, 3, 4), chiefly in 

 summer and fall, and it is in many cases evident, by the material used (see PL 

 XLI, Fig. 6) that the shutting up was done by the crawfish by clrpositing ])ellets 

 in the orifice. Often the "stopper" is not at the orifice itself, but a certain distance 

 (5 to G inches) below. In fall the stopper is made rather substantially and fills the 

 upper end of the hole for a distance of ('> to 10 inches (see PL XL, Fig. 9// at I>), and 

 such a filling cannot be accounted for by accidental falling in. 



]n my opinion the construction of the hole is the chief aim for which the craw- 

 fish works. For the removal of the clay and dirt an opening on the surface is 

 needed ; but wben the burrow is completed this opening is shut up again, and the 

 crawfish is content to remain inside, possibly for weeks or even months. This 

 affords protection for the crawfish and its young from enemies (snakes). Females 

 with eggs or young are almost always found in closi'd boles. It also affords neces- 

 sary quiet and seclusion during the moulting ])rocess (soft shells are generally found 

 in closed holes). It furthermore protects the hole from the disturbing influences 

 of rain and frost. Of C(jui-se it would not be advantageous to have the hole perma- 

 nently sealed, since the crawfish wants to get f)ut now and then (for mating, for 



