206 PTILOTA. 



the animal is not so dependent upon metamorphosis as in 

 the subsequent perfectly metamorphotic division. Thus 

 there are many species belonging to this section, which re- 

 main throughout their life in a state of imperfection ; of 

 which a common instance occurs in the HydrometridcB, or 

 water-measurers. These insects, which are to be observed 



Figs. 44, Apterous imago — 45, Winged imago of Velia rivulorum 



skimming along on the surface of the water, are generall}' 

 found destitute of the slightest rudiments of wings : they, 

 however, continue their kind, but occasionally certain indivi- 

 duals will be found in company with them with the wings 

 fully developed. Now it is impossible to regard the former 

 as pupge, because they have no rudiments of wings ; neither 

 can we consider them as larvse, because they are as large as 

 the winged individuals, and are able to propagate. Accord- 

 ingly they have been generally regarded as distinct apterous 

 species ; but a more extended investigation of these groups 

 of insects will prove the specific identity of these imperfectly 

 developed, but still perfect * (as regards their powers of pro- 

 pagation), individuals with the winged specimens. Thus, 

 there are many species, which, instead of being generally 

 wingless, are furnished \^ith short rudimental wings, and 

 which are nevertheless capable of reproduction ; hence, as 

 well as from the structure of the rudimental wings, it is 

 evident that they cannot be pupae, and yet it occasionally 



* " The true criterion of animal as well as vegetable perfection is the 

 ability to continue the species."— MacLe a. y, Horas Entomologic<£, p. 446, 



