The Simplest Insects 



59 



It is familiar knowledge that animals which live parasitically 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 as 

 organs of locomotion (wings, legs), and of Jj 

 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 superficial 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 worker 



tion of the ovarial tubes in three 



A P' e . ran &- *'/ apy ?i ft B ' 

 Lepisma; C, Campodea. (After 



Targioni-Tozzetti; much en- 

 larged.) 



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



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 insects 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 

 Apteran genera. A, Machilis; B, Xl . , . 



Nicoletia; C, Japyx. (After Tar- 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 



