DEVELOPMENT OF INSECTS. 



351 



Pig. 299. Embryo of Sphinx 

 much more advanced, h, heart ; 

 gr, ganglion; i, intestine; )>i, 

 rudimentary muscular bands run- 

 nins: to the heart ; *, stigma and 

 beginniiigof a trachea (t) ; rf,a 



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 ; 



-, , , , ,1 , 

 and at about thlS time 



fu_ O f irrtnofo onrl nir 

 ""6 StlgUldicl <ill< 



i 11 i-. p<5 nr iap nq 

 tionS f tlie uter 



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 moth, with thl 

 larva on hatching is still enveloped in the am- d ff| d lts ^ 

 nion. This is soon cast as a thin pellicle. their rndimen- 



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



. ., . ... * lip; at, anten- 



adult locust or grasshopper is the acquisition ot use ; ma, man- 

 wings. In such insects, then, as the Orthoptera ^a?, 1 first' ami 

 and Hemiptera, in which the adults differ from f c . on ; d 



Fig. 300. 

 Primitive 

 band or germ 



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, 



