DEVELOPMENT OF INSECTS. 



331 



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. 201. Ernbrvo of Sphinx , , , ,-. ,. 



much more advanced. A, heart ; and at abOllt tlllS time 



g, ganglion ; i, intestine ; m, ,-\ L- -i 



rudimentary muscular bands run- ED 6 Stigmata ailO. ail*- 



nins to the heart ; g, stigma and 4- 11 i- lf i< ! nl .i c(i oo invtio-ini 



beginning of a trachea (t) ; d.a. U V digmdr 



gland. Tliis and Figs. 293,295 fjo^of f] lo oiltor p-prm- 

 aftei- Kowalevsky. L fe ej 



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- Qj.0 



ter, as in the flea, 'or the expansion of the 1 jwp 



head and thorax and the convulsive movements \o 

 of the body, as in the grasshopper, burst the Fj g . o 93 _ 



shell asunder. The serous membrane is left in band" 



the shell, but in the case of grasshoppers the n f ot g 



larva on hatching is still enveloped m the am- segments in- 

 dicated, and 

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



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



adult locust or grasshopper is the acquisition of me mdf man- 



wings. In such insects, then, as the Orthoptera m^^rli and 



and Hemiptera, in which the adults differ from f^ c . on f n /' ax r" 



the newly hatched larva mainly in the posses- legs ; o*. ai>d 



J . i j i miual le s s - 



sion of wings, metamorphosis is said to be in- 

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

 i? complete ; the caterpillar, for example, is d biting insect,. 



