ON THE HABITS OF ANIMALS. 129 



migratory impulse seizes upon those great herds, 

 and they rush along the plains, cross rivers, 

 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 pro- 

 cession of caterpillars may frequently be ob- 

 served. They travel in single file, having a 

 leader; and 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 imme- 

 diately 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 communication with the leader. 



K 



