294 FLASHLIGHTS ON NATURE 



the larva is at first soft and free, hut that before 

 becoming a true pupa or chrysalis he passes through 

 an intermediate encased or "flax-seed" stage, in 

 which he performs some curious evolutions. The 

 young larva when he starts in life is whitish or 

 yellowish ; in the " flax-seed " stage he becomes a 

 rich chestnut brown, and seems externally quiescent. 

 But the fact is, he arrives at full growth in the 

 white form, and then leaves off feeding; his skin 

 now hardens and darkens, and he looks from out- 

 side very much like a pupa. Indeed, his outer 

 covering is now a sort of solid pupa-case, in shape 

 just the same as the original grub, hut more sombre 

 in colour. No. 6 shows you the portrait of the 

 grub in this curious intermediate condition. If 

 you compare it with No. 3, you will see that the 

 outer skin still preserves the original shape of the 

 fat young larva ; but that the enclosed grub him- 

 self, here shown as if the case were transparent, 

 has shrunk away from his own old skin, just as a 

 ripe nut shrinks away from its shell, to borrow 

 Mr. Enock's admirable phrase for describing the 

 process. And this strange shrinkage is connected 

 with a very curious fact in the eventful life-history 

 of the Hessian fly ; it tells us of a problem which 

 the grub has to face, and for which it has devised 

 a most unexpected solution. 



You remember that the young maggot had 

 necessarily to work its way head downward along 

 the stalk, in order to fix itself in the only place 

 where it can find the soft food needful for it, 

 between the sheath and the stem, where the tissue 



