The Simplest Insects 



59 



Fig. 88. — Diagrammatic figures 

 showing the segmental disposi- 

 tion of the ovarial tubes in three 

 .\pteran genera. A, J a pyx; B, 

 Lepisma; C, Campodea. (After 

 Targioni -Tozzetti; much en- 

 larged.) 



It is familiar knowledge that animals which live parasitical!}' on others, or 



which adopt a very sedentary life, show a marked degeneration of body 



structure, an acquired simplicity due to the loss of certain parts, such a.s 



organs of locomotion (wings, legs), and of 



orientation (eyes, ears, feelers, etc.). Thus 



the parasitic biting bird-lice (order Mal- 



lophaga, see p. 113), which live their whole 



lives through on the bodies of birds, feeding 



on the feathers, are all wingless and of gener- 

 ally simple superticial structure. They are 



nearly as simple externally perhaps as the 



Aptera, but we believe that they are the 



degenerate descendants of winged and in 



other ways more complexly formed ancestors. 

 Similarly certain species of insects in 



nearly all orders have adopted a life-habit 



which renders flight unnecessary, and these 



insects having lost their wings are in this 



character simpler than the winged kinds. 



Examples of such insects are the w-orker 



ants and worker termites, many household insects, as the bedbugs and fleas, 



f. and many ground-haunting forms, as some 

 of the crickets, cockroaches, and beetles. 



The Aptera, however, owe their sim- 

 plicity to genuine primitiveness; among all 

 living insects they are the nearest repre- 

 sentatives of the insectean ancestors. But 

 not all the Aptera are "simplest." That 

 is, within the limits of this small order a 

 considerable complexity or specialization of 

 structure is attained, although all the 

 Aptera are primitively wingless, as the 

 name of the order indicates. 



These in.sects develop "without meta- 

 morphosis " ; that is, the young (Figs. 90 

 and 94) are almost exactly like the parents 



Fig. 89.— Diagrammatic figures'show- except in size. They have simply to grow 

 ing the respiratory system in three larger and to become mature. In internal 

 JvS"„f' c!'/«^i ^'(.\hl"'-V^r'- Structure the simpler Aptera show some 

 gioni-Tozzetti; much enlarged.) most interesting conditions. Their internal 



systems of organs have a segmental character corresponding to the external 



segmentation of the body. The ovarial tubes, which are gathered into 



