via INTRODUCTION. 



We observe, also, that certain types, when hatched from the 

 eg-g resemble in appearance the parent, and finally assume the 

 characters of the adult after growth and repeated changes of skin. 

 In others the individual (larva) emerging from the egg bears no 

 resemblance to the adult, but after growth, accompanied with 

 several changes of skin, passes into a condition in which a body 

 similar to that of tlie perfect insect is covered by an integument 

 which is finally shed. This condition is called the pupa, during 

 vvhicli- the animal is sometimes active, sometimes inactive. 



In a few families of Coleoptera (Meloidce, Rhipiphoridai, and 

 Stylopidae, which are parasitic in their habits) there are two dis- 

 similar larval forms, separated by an inactive {pseudopupa) con- 

 dition, before the true pupa is evoluted: this method of develop- 

 ment is called Inj per metamorphosis. 



The three thoracic segments are either (1) -similar (except that 

 the middle and posterior ones bear wings), or (2) agglutinated 

 into one mass, or (3) the anterior one {pjrotlwrax) is freely mova- 

 ble, and the other two (mesothorax and meiathorax) closely con- 

 nected with each other and with the abdomen. 



The parts of the mouth are also modified in form so that the 

 maridibles and ma.xillaj are either free moving lateral organs fitted 

 for prehension and mastication, or are elongated, forming a suck- 

 ing tul)e of different construction in the different orders; in the 

 former case the mouth is said to be viandibulate, in tlie latter 

 hauslellale. The wings are also of varied structure. 



The embryological studies of insects are as yet not sufficiently 

 progressed to enable us to subordinate these coni})lications of 

 structure in such manner as to determine which orders are 

 higher and which lower. We can merely state in general terms, 

 that those having a perfect metamorphosis are the highest; those 

 having the thorax agglutinate, and those having the prothorax 

 free arc respectively higher than those in which the larval 

 equality of the three thoracic segments is preserved. 



The orders having numerous veins in the wings must also be 

 considered as lower than those liaving but few. 



The sub-class as. represented in the present geological epoch 

 may be divided into orders as follows: — 



