44 INSECT TRANSFORMATION 



development of the dragon-fly cannot be traced in detail here, 

 but there is an interesting variation from that of the grass- 

 hopper in that the germ-band grows so as to be folded into 

 the yolk, carrying with it a sheet of thin blastoderm which 

 forms the amnion, and lying for a while with its ventral aspect 

 towards the face of the egg opposite to that along which it 

 was originally formed. Then at a later stage, the embryo 

 reverts to its original position, bursting the amnion in the 

 process, and before hatching secretes a thin, firm cuticle which 

 ensheathes the appendages already definitely formed. The 

 egg-shell is ruptured (Fig. 23 A, B) by the swelling of the head 

 region of the embryo due to the action of a pulsating " cephalic 

 heart ' (Fig. 23 ch) connected with the gullet ; thus the 

 young insect enswathed in its cuticular sheath is hatched. 

 In a few minutes, or possibly in a still shorter period, by the 

 continued action of the " cephalic heart," this sheath may 

 be burst, and the larva creeping therefrom is ready to begin 

 its active life (Fig. 23 C, D). 



The young larva of a dragon-fly (Figs. 23 E, 24) has a broad 

 head with a pair of compound eyes already fairly prominent, 

 and short three-segmented feelers. The three thoracic 

 segments are closely alike with the legs relatively very long, 

 each foot consisting of a single segment bearing two claws. The 

 abdomen is short compared with that of the adult, broad in 

 the larvae of the more robust and larger dragon-flies, slender 

 in the young of the delicate damsel-flies (or " demoiselles ") ; 

 at the tail end are a pair of fringed appendages, and sometimes 

 a median one also. Turning again to the head, we notice that 

 the mandibles and maxillae are much like those of the adult 

 dragon-fly, but the labium is remarkably modified. The 

 sub-mentum and mentum (Fig. 24 sm, m] are both elongated, 

 the latter hinged to the former and the former to the ventral 

 head skeleton ; thus the organ can be folded so as to be 

 hidden beneath the head (Fig. 24 B, C, E), or can be stretched 

 out far in front of it (Fig. 24 D). At the extremity of the 

 mentum is a median lobe (Fig. 24 D, ml, probably representing 

 both laciniae and galeae) and a pair of externally-placed, 

 jointed, sharp, toothed processes (Fig. 24 D, mh), the modified 

 palps. By means of these, when the " mask ' (as this 

 strangely transformed labium is called) is stretched out, the 



