THE PROCESSIONARY MOTH. 589 



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feotly hexagonal throughout, although some of them are only at- 

 tached by one side, and are not pressed upon at either of the five 

 remaining sides. We find that the external angles are as sharp, 

 and their internal measurement as true, as those which occupy 

 the very centre of the bee-comb ; so that pressure is clearly not 

 the cause of the hexagon. That excavation is not the cause is 

 also evident, from the fact that the external cells can not have 

 been excavated, and yet are hexagonal. 



These examples, therefore, show that the hexagonal form can 

 exist without pressure. But, as if to show that pressure can exist 

 without producing the hexagonal form, we have the nest of the 

 Mischocyttarus, whose long, delicate, soft- walled cells are grouped 

 round each other, and yet retain their conical form, so that at any 

 part of them a transverse section would show a circular edge. 



The insect which makes this nest is rather long, measuring per- 

 haps an inch in length. The color is pale yellow and the abdo- 

 men is much elongated, and attached to a slender foot-stalk or 

 peduncle nearly as long as itself. Several of the cells have been 

 occupied by larvae which have begun to assume the pupal condi- 

 tion, as is shown by the white covers over their mouths. 



One of the most remarkable of these branch-building insects 

 is that which has been appropriately named the Pbocessionaet 

 Moth {Cneethocampa processioned). This curious moth lays a 

 number of eggs, mostly upon the oak, and as soon as they are 

 hatched the little creatures begin to form their home. 



Externally it is not unlike that of the brown-tailed moth, but it 

 differs in one respect, namely, that it is' not divided into separate 

 chambers, and has only one aperture. When the larvae sally out 

 for the purpose of procuring food, they spin guide-lines, as is the 

 case with many . other caterpillars. But, instead of going out 

 singly into the world, each to find its own food in its own way, 

 they march out in regular order, like a military party on a fora- 

 ging expedition. 



A single caterpillar is always the leader, and often is followed 

 by one or two others in Indian file. Presently, however, the cat- 

 erpillars march two deep, and, if a large number should be on the 

 move, the line is sometimes from five to six deep. They are all 

 very close to each other, so that the procession flows on in one 

 unbroken line, and, until the observer is close to it, he can not see 

 that its component parts are moving at all. 



