80 HISTORY OF INSECTS. 



these coverings are cast at the same time ; the interior one, 

 fine, semi-transparent, and delicately soft, must have been 

 observed by all who have paid any attention to the rearing 

 of Lepidoptera. Now the whole of the Necromorpha, as 

 far as has yet been ascertained, finally undergo a single, 

 and the whole of the Amorpha, on the other hand, a double 

 ecdysis. 



The Isomorpha, of which the common cricket is an ex- 

 ample, have no quiescent state ; nor can we find that they 

 possess any state precisely equivalent to that portion of 

 the lives of the two great groups we have been comparing. 

 Their whole existence between the egg and the imago con- 

 sists of a gradual series of approaches to perfection ; and 

 during this interval reproduction has been known to take 

 place. No character is yet discovered by which the 

 penultimate, antepenultimate, and prior states can be de- 

 termined. 



In the heterogeneous group, Anisomorpha, a group in 

 metamorphosis, as in all other characters, equally related 

 to the other three, we find a typical and distinct section in 

 the dragon-flies. These, like the Isomorpha, have no qui- 

 escent state : their preparatory state is aquatic, active and 

 voracious: when arrived at the period for assuming the 

 imago, they leave the water, and fixing their feet firmly to 

 a slender stick or blade of grass, emerge from a double 

 skin and fly away. The exterior skin is hard, corneous, 

 and brittle ; the interior soft, fine and pliable. The May- 

 fly, one of the Anisomorphous insects, has a metamorphosis 

 still more striking, and one that has been deemed anoma- 

 lous and unaccountable. In the antepenultimate skin it 

 leaves the water, and attaches itself by the legs like the 

 dragon-fly. Its antepenultimate skin then opens on the 

 back ; the insect emerges and flies away, leaving that one 

 skin only that beautifully delicate skin which the dra- 



