194 LECTURE XI Y. 



ascend hills, and go in one undeviating line to 

 some far-distant locality, overturning tents and 

 other obstructions in their way. So it is also 

 with the land-crabs of Jamaica. When the 

 season arrives, they quit the upper country and 

 make a rush towards the sea-shore in a direct 

 line, and nothing stops their progress, so strong 

 is the migratory instinct. 



This extraordinary impulse is also possessed 

 by some insects. In Australia a migratory 

 procession of caterpillars may frequently be 

 observed. They travel in single file, having a 

 leader; arid each is so close to its predecessor 

 as to convey the idea that they were united 

 together, moving like a living cord in a con- 

 tinuous line. If one caterpillar should be taken 

 from the middle of the line, the one immediately 

 before him suddenly stands still, then the next, and 

 then the next, and so on to the leader. The same 

 takes place at the other end of the line. When 

 the caterpillar which is removed gets into the 

 line again, the whole move forward as at first, 

 thus apparently having some means of communi- 

 cation with the leader. This was not a solitary 

 experiment, but has been repeatedly tried during 

 the progress of these insects, and proves the 



