252 CHAPTERS ON EVOLUTION. 



XII. 



THE EVIDENCE FROM THE LIFE-HISTORIES 

 OF INSECTS. 



WHEN the development of an animal or plant is duly studied, 

 one or two chief aspects of such a subject fail to be considered 

 hy the biologist. Either the young organism has been converted 

 directly into the likeness of its parent, or it has assumed the pa- 

 rental form indirectly and through a series of transformations more 

 or less distinctly marked. In other words, the young form has 

 emerged upon the stage of life in the guise of its parent, or it has 

 appeared first in a shape and under an appearance not recognisable 

 as belonging to the race it has sprung from. In the latter case, 

 changes of greater or less extent convert the young being into the 

 likeness of its progenitors ; and when such transformations occur in 

 the life-history of an animal or plant, it is said to undergo " meta- 

 morphosis." Every one, for instance, knows that the butterflies of 

 the garden do not emerge from the egg as winged insects, whilst 

 common information is able to assert that they pass through the larval 

 or "grub" stage and also through the chrysalis form before becoming 

 the perfect insects. So, also, the flies begin their life as maggots ; 

 and the bees and beetles, with other insects, exhibit like stages to the 

 butterflies in the course of their development. Furthermore, a frog, 

 as we have seen, practically begins life as a fish, breathing first by 

 external and then by internal gills. Sooner or later, however, limbs 

 are developed ; the gills are replaced by lungs ; the tail disappears ; 

 and the tailless condition of the frog race is finally assumed with its 

 emergence upon the land. Insects and frogs not to speak of other 

 animals, such as crustaceans, whose history has been already discussed 

 in a previous chapter are therefore said to undergo "metamorphosis." 

 Sundry questions not unnaturally rise in the mind which atten- 

 tively considers such phenomena in the animal world. Firstly, there 

 is the plain question, " Why do some animals undergo metamor- 

 phosis and others not ? " Then, secondly, may be asked, " What is 

 the meaning of metamorphosis?" or more primarily, "Can any 

 meaning be assigned to this process ? " As we have frequently had 

 occasion to point out, such questions receive no aid or solution from 

 that philosophy which maintains, as an article of unquestioning faith, 

 that the living belongings of this world came forth fashioned in all 



