METAMORPHOSIS. 



i 



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FIG. 30. 

 A. wingless mature Cockroach. 



metamorphosis and which are really intermediate between these two 

 groups; but they are not common and we are unlikely to meet with 

 them. We shall find large and distinct groups of insects which have a 

 metamorphosis, and equally large and 

 distinct groups which have none ; 

 every student should know at once 

 whether an insect has or has not a 

 metamorphosis. 



Before proceeding to the next sec- 

 tion, we may draw attention to a 

 few points. 



All perfect insects, i.e., ima- 

 gines, have wings, or should have ; 

 there are many exceptions to the 

 rule and in many insects the wings 

 are not fully developed. This is more common in insects which have no 

 metamorphosis than in those which pass through the pupa stage. 



Such insects which look immature can be known as mature if seen 

 coupling. None but imagines, i.e., perfect insects, can couple or reproduce. 



On the other hand, any insect with fully developed wings, i.e., with 

 wings with which it can fly, is an imago and will not grow any more. A 

 small flying grasshopper cannot be a young locust or become anything 

 else. A small beetle cannot grow into a large beetle. Whatever its size, 

 a winged insect is full grown and will not do more than lay eggs. This 

 is an absolutely invariable rule. 



In later paragraphs, the life history is stated in greater detail and 

 some of the many exceptions to general rules are discussed. In entomo- 

 logy, as in all other branches of biology, the general rules are abundantly 

 proved by their exceptions. There are very few general statements that 

 can be made to which there are not many exceptions. We can say 

 generally that all insects are hatched from eggs, but there are very 

 numerous exceptions ; equally we can say generally that mature insects, 

 like other creatures, are of two sexes and that the process of reproduction 

 is dependent upon both sexes ; even this statement is not true of all insects. 

 It is necessary to guard against hard-and-fast rules and generalities 

 in dealing with insects ; they are valuable as aids to memory and the 

 imagination, inevitable in class rooms and books, but they must be carefully 

 used outside the class room. Nature has no cast-iron rules, and the more 

 we study nature the more we find an infinite variety that laughs at our 

 generalisations. One group shades into another ; the habits of one class 

 are linked to those of another by insensible gradations ; no two species 



