THE DEVELOPMENT OF INSECTS. 



59 



The body is so bent upon itself that the extremities of the 

 second maxillae just overlap the tip of the abdomen. 



The two limbs of the labium are now placed side by side, 

 with the prominent spinous appendage on the outer edges of 

 the tip. These spines are the rudiments of the labial palpi. 



The general form of the embryo at a still later period (Fig. 

 61), on being taken from the egg and straightened out, re- 

 minds us strikingly of 

 the Thysanura, and, in 

 these and other re- 

 spects, tend to prove 

 that the Podurse and 

 Lepismse, and allied 

 genera, are embryonic, 

 degraded forms of Neu- 

 roptera, and should 

 therefore be considered 

 as a family of that sub- 

 order. Seen laterally, 

 the body gradually ta- 

 pers from the large N 

 head to the pointed ex- 

 tremity. The body is 

 flattened from above 

 downwards . At this 

 stage the appendages 

 are still closely ap- 

 pressed to the body. 



Just before the ex- 

 clusion of the embryo, 

 the legs and mouth- 

 parts stand out freer Fig. 62. 

 from the body. The labium, especially, assumes a position at 

 nearly right angles to the body. The antennae, mandibles, 

 and maxillae have taken on a more definite form, being like 



FIG. 62. The larva just hatched and swimming in the water. N, ventral cord or 

 nervous ganglia; D, dorsal vessel, or "heart," divided into its chambers. The 

 anal valves at the end of the abdomen, which open and shut during respiration, are 

 represented as being open. Both of the dotted lines cross the tracheae, x, net- 

 work of the tracheae, surrounding the cloaca. 



