DE GENERA TION, 



383 



latter want is seen even in those cases in which one sex alone of a 

 particular insect species assumes the habit in question. An excellent 

 illustration of such a fact, and also of the extreme modification of 

 form which may accompany the degeneracy of highly organized ani- 

 mals, is found in the history of the insects collectively known as 

 Streiysijotera, and of which the genus Stylops is the best-known exam- 

 ple. The male stylops (Fig. 13, a) is an active insect, possessing a 



Fia. 13. Stylops. (Fig. c shows the Stylops, in outline, within the hody of the Bee ; and Fig. b 



shows the Stylops removed from the body of its host.) 



single pair of wings. These wings are the hinder pair ; the front pair 

 being represented by a pair of twisted organs (w), which illustrate 

 wing-degeneration, possibly through disuse. Both males and females 

 as they leave the egg are small, active, six-legged beings (<:?, e), which 

 crawl about on the bodies of bees. Carried into the hive, the young 

 stylops behave like the proverbial viper, injuring the community 

 which gives them shelter by boring their way into the bodies of lar- 

 val or infant bees. Here the young stylops, casting their skin, become 

 in the larval interior sluggish, footless grubs. Each possesses a mouth, 

 small jaws, and a digestive system of simple construction. Mean- 

 while, bee-development progresses ; and, as the larval bee passes 

 through its chrysalis state with its stylops-lodger contained in its inte- 

 rior, the latter thrusts the front extremity of its body from between 

 two of the hinder body-segments of the bee. Then the male stylops, 

 undergoing development in this position, becomes the winged insect (a) 

 and passes into the world. The female stylops (c), on the other hand, 

 remain in their places on the bees. They undergo but a slight change 

 of form, persisting as mere sac-like bodies (c), without legs or diges- 

 tive system (5), and develop in their interior the eggs from which suc- 

 ceeding generations of stylops will be produced. Such a case of abso- 

 lute degeneracy is all the more remarkable in view of the facts that it 



