308 University of California Publications in Zoology [Vol. 19 



As the isopods crawled over the edges of their bore, however, scratches 

 were seen to be made by the feet in the thin edge of chalk around the 

 mouth of the bore, and certain longitudinal scratches found in the 

 bores may have been made by the claws or by the uropods. The 

 softening of the chalk block by its immersion in water may have 

 facilitated the making of these adventitious scratches. 



The effective boring is, however, done with the mandibles. Grip- 

 ping the sides of the hole by striking the claws of its feet into the 

 chalk, the isopod spreads its mandibles apart and drives them into 

 the chalk near the head of the bore. At the height of this exertion 

 the anterior end of the body of the animal is pressed down so tensely 

 as to cause the surface of the back in the region between the head and 

 the anterior thoracic segment to be indented. At the next moment 

 the fragment of chalk is bitten off, handed back by the palpi and 

 the feet until under the abdomen, and is then washed out of the 

 bore by the current of water set up by the swimmerets. By contin- 

 ually turning around in the bore the shape of the hole is made cylin- 

 drical and its size is automatically determined by the size of the borer. 

 So energetic and efficient was the work of this little borer that a 

 quiescent isopod lying in the mouth of another hole closely adjacent 

 to the hole under observation was covered with chalk dust, as if with 

 snow, in the course of twenty or thirty minutes. Boring into the 

 chalk is undoubtedly more easily and rapidly accomplished than 

 boring into sandstone or tuff, but there is no reason to suppose that 

 the boring process in nature is essentially different from that observed 

 in the laboratory. 



Disturbed by the opening of the window in its bore, the particular 

 isopod observed during this process was seen to turn around in 

 its bore occasionally and to work at the mouth of the bore or at 

 the sides of the hole, evidently reaming out some narrow portion to 

 the proper size. This confirms a former suggestion that in nature the 

 growing animal probably occupies but one hole during its lifetime, 

 enlarging this hole as may be necessary. In nature also the boring 

 process is probably not a slow or tedious one, but is fairly rapid while 

 in progress, though interrupted by many periods of quiescence after 

 the original entry has been made into the rock. 



In setting up the currents by which the hole is cleaned the water 

 seems to enter the hole in a diffused stream and is drawn gently about 

 the head by suction from the action of the swimmerets. The sides 

 of the body fit down closely against the side of the hole so as to confine 



