OKIGIN OF LARVA-FORMS. 



127 



as insects, in the well-known walking-stidr-insects, allies of the 

 grasshoppers (fig. 32), which resemble a more or less dried-up 

 twig or shoot. Many of these species are wingless, so that they 

 bear a wonderful resemblance to the larvse of other, winged 

 forms. If then we assume that the wingless forms are the 

 progenitors of winged forms, the origin of the winged forms 

 may be very well explained by the further assumption that the 

 optimum temperature necessary for maturing the e^s may 

 have been raised so much as to afford more time for assimilar 



Fig. 22.—FJtasma sp., a wingless orfhopterous insect. 



tion and growth, and consequently for more extensive modifica- 

 tions of structure. If, on the other hand, we regard the wing- 

 less species as the later form and derived from the winged 

 species, their origia may be easily explained by assuming that 

 the optimum of temperature for the maturing of the eggs was 

 lowered, while the optimum for growth remained the same. 

 For we know that in many cases, particularly among insects, 

 the life of the individual ends as soon as the eggs are mature 

 and deposited, and that the performance of this function seems 



