42 RELATION OF THE LAEVA TO THE IMAGO. 



to tlie common primitive form, we must also expect 

 that their mode of development will agree better with 

 that of the primitive form than, for example, that of 

 the Lepidoptera, in the same way that somfe of the 

 prawns (Peneus), approaching most closely the primi- 

 tive form of the Decapoda, have most truly preserved 

 their original mode of development. ISTow, the majority 

 of the Orthoptera quit the egg in a form which is 

 distinguished from that of the adult insect almost 

 solely by the want of wings ; these larvae then soon 

 acquire rudiments of wings, which appear more strongly 

 developed after every moult. Even this perfectly 

 gradual transition from the youngest larva to the 

 sexually mature insect preserves in a far higher de- 

 gree the picture of an original mode of development, 

 than does the so-called complete metamorphosis of 

 the Coleoptera, Lepidoptera, or Diptera, with its 

 abruptly separated larva-, pupa-, and imago-states. 



" The most ancient insects would probably have most 

 resembled these wingless larvae of the existing Orthop- 

 tera 



"The contrary supposition, that the oldest insects 

 possessed a ' complete metamorphosis,' and that the 

 * incomplete metamorphosis ' of the Orthoptera and 

 Hemiptera is only of later origin, is met by serious 

 difficulties. If all the classes of Arthropoda (Crustacea, 

 Insecta, Myriopoda, and Arachnida) are, indeed, all 

 branches of a common stem (and of this there can 

 scarcely be a doubt), it is evident that the water- 

 inhabiting and water-breathing Crustacea must be 

 regarded as the original stem from which the other 

 terrestrial classes, with their tracheal respiration, have 

 branched off; but nowhere among the Crustacea is 

 there a mode of development comparable to the ' com- 

 plete metamorphosis ' of the Insecta, nowhere among 

 the young or adult Crustacea are there forms which 

 might resemble the maggots of the Diptera or Hymen- 

 optera, the larvse of the Coleoptera, or the caterpillars 

 of the Lepidoptera, still less any bearing even a dis- 



