CLASSIFICATION OF INSECTS. 49 



We have used Lepisma instead of Campodea in our 

 comparisons, because it is larger and easier to obtain, 

 and in some respects, also, it approximates perhaps 

 more obviously to the ordinary flattened larvae of the 

 more generalized forms of insects. It is closer also 

 to the larvae of the cockroaches, which are regarded 

 by Scudder and some entomologists as the most prim- 

 itive of existing winged forms, and are known to be 

 among the oldest in geologic history. This active 

 hexapod (Lepisma) has a thorax consisting of three 

 equally developed simple rings without secondary 

 sutures or wings, and a broad abdomen whose junc- 

 tion with the thorax is unconstricted. These pecul- 

 iarities are permanent adult characters, which are apt 

 to reappear during the transient stages of larval growth 

 in species and groups of all the orders from II. to XI. 

 inclusive. 



The mouth parts of Lepisma and Campodea belong 

 to a peculiar type of generalized structures, being set 

 deeply in the head, and capable of being employed 

 both for biting and suction. They are, however, more 

 nearly allied in structure to the biting^ than to the 

 more highly speciaHzed forms of sucking mouth parts, 



"On the Origin of Insects." Joiirn. Linn. Soc, Vol. XL, 



1873- 



Origijt and Metamorphoses of Insects. Nature Series, 1873. 



Monograph of the Colleinbola and Thysamira, Chap. III., 



1873- 



Origin and Metamorphoses of Insects. Book form. 1874. 



Mayer, P. " Ueber Ontogenie und Phylogenie der Insekten," 



Zeits.f Nat., Jena, Vol. X., 1876. 

 ^ See Packard, Our Common Insects, pp. 129-132; also, 

 American N^aturalist, Vol. V., p. 91. 



