XOTES OX Till: HKIIAYIOK OF Till; I- IDIH.KK CKAH. 



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always a simple tube. It is difficult to say to what conditions 

 may be due the marked individual differences in the shape of the 

 burrows, as the external conditions on a horizontal bank of pure 

 sand seem to be perfectly uniform for all individuals. Referring 

 them to the different individuality of the crabs may be true, but 

 probably it means nothing more than our complete ignorance of 

 the causes. 



FIG. i. Different types of natural burrows. 



To be able to watch closely the process of burrowing we must 

 observe it in the laboratory. In cylindric glass-jars (6 inches in 

 diameter, 9 inches high) half filled with wet sand the crabs 

 struggle madly and try to escape by climbing on the glass wall, 

 in which they are of course unsuccessful. The animals remain 

 near the wall and particularly near the most lighted spot of it. 

 After some time the movements become slower, the crab gives 

 up its attempts to escape and it keeps quiet for a while in its 

 normal position. Finally it begins to dig. The individual 

 behavior may be very different. Some crabs start their work 

 after a few minutes, others roam around the jar for hours and 

 even days. Some remain motionless for many hours, others 

 move perpetually and struggle for escape. Some may walk 

 around the wall showing no particular predilection for the lighted 

 side^some again remain for a long time at the spot nearest to 

 the window. There is a slight difference between the sexes, the 

 females being more shy on the average and starting the work 

 sooner. The mode of working is also somewhat different in 

 both sexes, which will be mentioned later. 



