THE AMERICAN ENTOMOLOGIST. 



261 



Fig. 137.] 



Mandible of Phylhcttis- 

 tis (after Chambers). 



we see it accompanied by articulated legs 

 — always so in the pupa state. There 

 seems to be a regular ascending scale of 

 evolution epitomized, for instance, in Lit/i- 

 ocoUetis. The fact that 

 the articulated legs al- 

 ways succeed the mem- 

 braneous ones ; that 

 what I have called the 

 second form of trophi 

 always succeeds the 

 first, and is succeeded 

 by that of the pupa 

 and imago, seems to indicate that the 

 organs which characterize the later forms 

 have been acquired later in the evo- 

 lution of the species than those which 

 characterize the first form. But if this be 

 so, then the earliest form of insect must 

 have been, if not like the larva of Phylloc- 

 in'stis, yet much more vermiform than it is 

 sui)posed to have been by many entomolo- 

 [Fig. 139.] gists. By the earliest 



form of insect we can, 

 on a theory of evo- 

 lution of all organic 

 forms from one or a 

 few elementary ones, 

 Labium of first form in of coursc, Only mean 



Litnocolietis rcotnieUa\a,i- ^ 



ter Chambers). SOmC Stage at which 



evolution was arrested or became stationary 

 so long that the characters of that stage 

 were impressed on all of its descendants. 

 Whether there ever was such a stage, what 

 caused the arrest at that stage, how long it 

 lasted, and why there were so few such 

 stationary stages as are indicated in the 

 articulate sub-kingdom, are matters that we 

 do not now inquire into. If there ever was 

 [Fig. 140.] such original insect 



form, it must have pos- 

 sessed all of the organs 

 that are common to the 

 insect class — its de- 

 scendants. It must 

 Labium of first form in have been a typical in- 



Leucanthiza ai'iphicarpe~ 



<r/£>//>//<j (after Chambers). sCCt. It mUSt have pOS- 



sessed labrum, mandibles, maxillae, max- 

 illary palpi, labium, labial palpi, antennas, 

 eyes, articulated legs, and wings or their 

 originals (branchiae ?). If so, then all lar- 



[Fig. 141 



[Fig. 143.] 



VK must be degraded forms in so far as 

 any of these organs are wanting ; and 

 larvEe with membraneous legs and trophi 

 of the first form must be greatly degraded. 

 We can imagine a process of degradation 

 from this typical insect 

 to such a larva as that 

 of Phyllocnistis. Sir 

 John Lubbock sup- 

 poses the original in- 



SPrt fnrni tn havp hppn Labium of first form in 



sect loim 10 nave oeen p,,yii„,„Mj^ vUi/oUMa 

 something like Campo- '^f'" Chambers), 

 ilea, with mouth parts of a somewhat rudi- 

 mentary character, capable of producing 

 by evolution either the mandibulate or 

 haustellate type. When we see how readily 

 even the most decidedly mandibulate lar- 

 vae are metamorphosed simply by the rapid 

 growth of some organs, and the absorption 

 of others into haustellate butterflies and 

 moths, it seems unnecessary to resort to 

 an original form with equivocal or undevel- 

 oped trophi. It seems 

 more probable that 

 the original form of 

 insect had all of the 

 mouth jjarts well de- 

 veloped. 



But if this be so, how 

 are we to account for 

 the diverse facts presented to us by the 

 leaf-mining larvae ? So far, at least, as 

 living in a mine and feeding on the paren- 

 chyma are concerned, the conditions of 

 existence have been the same, no doubt, 

 for ages ; but how various has been the 

 course of development. Upon what dif- 

 ferent variations natural selection must 

 have seized, and with 

 what different results 

 and how singular that 

 the right variation to 

 produce the required 

 result should have hap- 

 pened just at the right 

 time, and in so many 



/-nc^.c -It- rlif^ cam*^ Labium of first form in 

 cases at tne same Ornix frumvorella i:.<.iK^ 



time ! Thus, the orig- Chambers), 

 inal larval insect, in order to become 

 Phyllocnistis, must have lost its maxillae, 

 and its palpi; have had the form of its 



Labium of first form in 

 LithocolUiis guttijinitet- 

 la (after Chambers). 



[Fig. 143.] 



