34 



INTRODUCTION. 



cells similar to the leucocytes or white corpuscles of the blood ; 

 the intermediary agents in histogenesis are portions of tissue 

 existing in the larval state incorporated with the different organs, 

 or possessing a connection therewith even when they are to a 

 great degree separated therefrom." Histolysis of the muscular 

 tissue appears to be a sort of inflammatory process, during which 

 the phagocytes attach themselves to, or enter, the tissues which 

 are to be disintegrated, and by which the larval structures are 

 broken down into a creamy substance, the buds or germs from 

 which the new organs are to be developed being exempt from the 

 destruction. These buds grow as they are liberated, and so by the 

 two processes the new creature is formed. This is probably much 

 the same in principle as the ordinary growth of the tissues, only 

 more pronounced and evident through the greater rapidity of the 

 action in these particular transformations (vide Sharp, op. ext. v, 

 p. 165). 



We need not here enter into the interesting question of em- 

 bryology ; those who desire to do so should consult the works of 

 Graber, who has worked out the embryology of a species of Liria 

 (Chrysomelidve), and others. 



Phylogeny. 



The earliest known insects belong to the Hemiptera, Orthoptera, 

 and Neuroptera, and to an extinct Neuropterid order Palreo- 

 dictyoptera ; the types are strongly differentiated and they are as 

 well characterized for the most part as any insects now existing ; 

 nor are there any transitional forms to bridge over the gap 

 between the Coleoptera and other orders. Prom the very earliest 

 time of their appearance in geological strata the insects of this 

 order have undergone no appreciable change ; the period at which 

 they first appeared is somewhat doubtful, but the evidence 

 tends to prove that none existed during the Palaeozoic period, 

 the records being extremely meagre, and the insects described 

 being probably not coleopterous. In the present state of our 

 knowledge we cannot with any certainty say that the order ap- 

 peared before the Mesozoic period. In the Jurassic period (Lias 

 and Oolite) we find beetles abundant and far more numerous than 

 the insects belonging to any other order ; this was the age of the 

 great Saurian reptiles, yet the beetles co-existing with these appear 

 to belong to the same families and genera as those living at the 

 present time. In the Khastic beds insect remains have been found 

 in such abundance that the beds containing them have been called 

 the " Insect Limestone." The following families, among others, 

 are represented : — Scarab^eiDjE, Carabid.e, GrYRiNiDiE, Hydro- 

 philid^:, Lathridiidje, BuprestiDjE, ElateridvE, Cantharid^:, 

 CuRCULiONiDiE, and Chrysomelid.e. The Longicornia, Staphy- 

 liniile, and Coccijnellid.e appear to be altogether absent, as 

 well as the Xylopiiaga, the deficiency of the latter being 



