CLASSIFICATION OF INSECTS 



EMBRYOLOGICAL DATA. 



I. General Considerations. 



The various classifications of Insects which have been proposed by zoologists 

 rest either on considerations derived from their external characters and form, and 

 in part from their internal structure, or on the various modes of their development 

 from the egg. The earliest writers on classification availed themselves principally 

 of the number and structure of their wings, to divide the numberless insects into 

 several general divisions, and such an arrangement, as finally adopted by Linnaeus, 

 has prevailed to a great extent, sometimes modified by the introduction of some 

 smaller groups, which have been more generally admitted by English writers than 

 by those of the Continent of Europe. 



Fabricius introduced an entirely new view of the subject, di-\idmg the insects 

 according to the structure of the organs by which they take their food, and the 

 various structures and degrees of complication of the jaws became the foundation 

 of his system, which he not only applied in a general manner, but worked out in 

 all its details, assigning even to the smaller divisions characters derived chiefly 

 from the peculiar form of those parts. 



More recently the metamorphosis of insects has been made the foundation of their 

 classification, and they have been grouped according to the extent of the changes 

 they undergo from the egg, and according to the condition in which the young 

 animal remains for a time before it has arrived at its complete perfect growth. 



According to these views, those insects that are hatched from the egg with a form 

 very similar to the full-grown perfect animal, and which undergo slight or only 

 partial changes during their growth, such as the additional development of wings, 

 or which remain active throughout their metamorphosis, have generally been con- 

 sidered as belonging to one and the same great division, and have been brought 

 together as insects without metamorphosis, or with imperfect metamorphosis. On 

 the other hand, such insects as are hatched from the egg in the form of a maggot, 



