CH. XVI."] 



THE CATERPILLAR. 



271 



sometimes form single files for some length ; then 

 double and triple ones ; each being - equal in number 

 to the single one, as represented in the figure. The 

 leader of these "processionaries" does not seem 

 to differ from the body of its companions either in 

 size, shape, or colour ; nor does there seem to be a 

 natural leader. The first that happens to quit the 

 nest appears, from that circumstance alone, to be 

 considered as the chief; the rest follow in his train. 

 Where the mass is so compact, it seems indispen- 

 sable that the movement should be regulated with 

 the greatest precision ; otherwise a degree of con- 

 fusion would ensue which would greatly impede, if 

 not entirely stop, their progress. Accordingly, no- 

 thing can surpass the uniformity and regularity ob- 

 servable in their march : whatever be the route of 

 the leader, the others follow precisely the same steps. 

 If this leader should ascend to a certain height and 

 then descend, each rank goes to the identical spot 

 before it begins to descend ; if it should halt, the 

 progress of the rest is immediately arrested : their 

 march presents an instance of uniformity so com- 

 plete as to render it difficult at first sight to conceive 

 that the waving line of living creatures which is 

 seen to wind in a thousand figures, can possibly be 

 composed of so many separate individuals. 

 Another tribe of caterpillars, called by Reaumur 



