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 
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 Fl showin^the ag s r egmental : dfspo’S 
which renders flight unnecessary, and these tion of the ovarial tubes in three 
insects having lost their wings are in this ^f s Z, g c"camfodea Py (klter 
character simpler than the winged kinds. Targioni-Tozzetti; much en- 
Examples of such insects are the worker 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 
Nicoletial 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 
