AND THE LOWER ANIMALS. CO 



own lives, protect and defend those of the whole com- 

 munity. Looking at it from a mode-of-life point of 

 view, Ave may say that incomplete metamorphosis pro- 

 duces a series of new beings. 



Normal metamorphosis may be as it were dimi- 

 nished either by the premature acceleration of certain 

 parts, or from an arrest in their development, or from 

 their entire absence. Each of these causes acting 

 separately alters the phenomenon differently; when 

 united, they suppress it completely. An insect which 

 undergoes no metamorphosis, departs so widely from 

 the ideal type, that it may be considered as external 

 to the class to which it belongs, if we view it in a 

 physiological aspect; and its exceptional nature is 

 represented by negative characters. It never pos- 

 sesses wings, and consequently is never, properly 

 speaking, a complete insect; for organs of flight 

 belong as exclusively to insects among invert ebrata, 

 as they do to birds among vertebrata, and they are 

 quite as characteristic of one group as of the other. 



Besides, as we have already seen, the existence of 

 wings and their functional development are closely 

 associated with metamorphosis. They never exist in 

 the larva, nor are they to be found even in the 

 nymph ; they only make their appearance at the very 

 last stage of the animal's existence. 



All insects of powerful flight, and which can remain 

 on the wing for a considerable time, have to undergo 

 metamorphoses; no insect whose metamorphoses are 

 incomplete, not even excepting the celebrated voyager 

 grasshopper,* is possessed of these advantages. On 



# The voyager grasshopper (Acriclium migratorium) is that species 

 of the family Gryllidas whose heavy columns often ravage entire 



