DEVELOPMENT OF INSECTS. 



351 



appendages bud out from the under side of the primitive 

 band, and antennae, jaws, legs, ovipositor (or sting), and the 

 abdominal feet of caterpillars are at 

 first all alike. Soon the appendages 

 begin to assume the form seen in 

 the larva, and just before the insect 

 hatches the last steps in the elabora- 

 tion of the larval form are taken. 



As to the development of the in- 

 ternal organs, the ner- 

 vous system first origi- 

 nates ; the alimentary 

 canal is next formed ; 



Fig. 299. Embryo of Sphinx , , , , , , . , . 



much more advanced, h, heart ; and at about this time 



g, ganglion ; i, intestine : m. xv > i_ T 



rudimentary muscular bands run- the Stigmata and air- 



at 



arse as nvagna- 

 193 - 296 tionsof the outer germ- 

 layer. The development 



of the salivary glands precedes that of the uri- 

 nary tubes, which, with the genital glands, are 

 originally offshoots of the primitive digestive 

 tract. Finally the heart is formed. 



When the insect hatches, it either cuts its way 

 through the egg-shell by a temporary egg-cut- 

 ter, as in the flea, or the expansion of the 

 head and thorax and the convulsive movements 

 of the body, as in the grasshopper, burst the 

 shell asunder. The serous membrane is left in 

 the shell, but in the case of grasshoppers the 

 larva on hatching is still enveloped in the am- J?gJJ ts 

 nion. This is soon cast as a thin pellicle. their d ' 



The principal change from the larval to the ages, c, upper 



.,,., % .1 ! .e "P 5 at, anten- 



adult locust or grasshopper is the acquisition 01 n se ; md, man- 



wings. In such insects, then, as the Orthoptera 



and Hemiptera, in which the adults differ from 



the newly hatched larva mainly in the posses- 



sion of wings, metamorphosis is said to be in- 



complete. In the beetle, butterfly, or bee, the metamorphosis 



is complete ; the caterpillar, for example, is a biting insect, 





Fig. 300. 

 Primitive 

 band or germ 



