18 SOME SOUTH INDIAN INSECTS, ETC. [CHAP. II. 



have mouth-parts which combine the biting and sucking types. 

 Nor is it always easj to draw any strict line between insects 

 having "complete" and "incomplete" metamorphosis, thai is to 

 say, between those insects having a larva differing greatly from 

 the adult and separated in time from the adult by a resting (pupal) 

 stage and those in which the larval stage is mainly sepal 

 appearance and time from the adult by the absence of wings and 

 lack of any pupal period. Termites, for example, cannot be said 

 to undergo any complete metamorp # hosis, in the ordinary accepta- 

 tion of the term, yet, in some species at least, there is a period or 

 periods of "nymphosis" scarcely distinguishable from a true 

 pupal period as regards quiescence and structural change. 

 Aleurodidae also are closely allied in all respects to the Rhynchota, 

 yet they possess a quiescent pupal stage, whilst in their near 

 relatives, the Coccidae, a definite pupal stage occurs in the case of 

 niaks, but not in females, of the same spcries. In other cas 

 in the females of some glow-worms, even when the metamorphosis 

 is nominally "complete," there is scarcely any notable difference 

 between the larval and the final form of the insect. 



As a matter of fact, it is generally easier to divide insects more 

 or less arbitrarily into groups than it is to divide them into Orders 

 by any one system of classification. Such a remark is an oi>\ ious 

 truism, but yet even at the present day one still sees attempts to 

 apply some particular rule-of-thumb method to the classification of 

 insects. The truth is, of course, that insects have gradually 

 evolved during a period of millions of years, from one common 

 ancestor or perhaps from several different types, and that in some 

 cases groups of modern insects originally of the same stem have 

 become extremely different in structure, metamorphosis or other 

 conditions, whilst in other cases groups originalh distinct may by 

 convergence have assumed details of structure, metamorphosis, 

 etc., which at first sight are deceptively similar. 



Xo fossil insects appear to have been found in India, but Geology 



tells lis that insects existed in 

 almost the earliest times (Low- 

 er Silurian) of which any fossil 

 records have come down to us. 

 The very earliest insects known 

 are perhaps hardly referable to 

 any of the orders now extant 

 1 odia />n.-.a>/_ but the three modem Orders 



'tcta, of Orthoptera, Neuroptera and 



'•Measures. He miptera were already repre- 

 sented in the Devonian pi nod 

 by tonus which, though not strictly comparable with the modern 



