246 SECTION D. ARTHROPODA. 



3. Some points in the classification of Insecta 

 Hex A POD A. 



By Dr D. Sharp. 



Although there is a generally accepted opinion amongst 

 zoologists to the effect that the branch of ontogen}^ called meta- 

 morphosis is of great importance in the study and classification 

 of Insects, yet it is certain that the efforts that have been made to 

 utilise the known facts are far from final. The terms Ametabola, 

 Hemimetabola, etc. that have been used are not sufficiently definite 

 for taxonomic purposes, or for a lucid consideration of the subject. 

 One point of considerable importance has escaped attention, and 

 this point I think will be found to furnish us with an additional, 

 definite criterion as to the metamorphosis of insects. It is that in 

 one set of cases the wings are developed outside the body, while in 

 another set of cases they are developed inside the body and become 

 suddenly external. 



The number of insects that can be correctly said to be entirely 

 destitute of the phenomena of metamorphosis is very small indeed. 

 As all of us know they are called Ametabola. For those that 

 exhibit the phenomenon of metamorphosis Packard has recently 

 proposed to adopt four categories, viz. Manometabola, Here- 

 metabola, Hemimetabola, Holometabola ; these terms, in addition 

 to that of Ametabola and to that of the condition of acquired 

 ametabolism (indicated by Lang but apparently as yet without 

 name), make no less than six categories of metamorphosis ; and in 

 addition to them we meet with other terms, such as Paurometabola. 



These terms indicate the amount of metamorphosis. But they 

 do so in only a very vague manner, and I think we shall gain by 

 considering them as of subordinate importance to the nature of the 

 wing development. 



On the accompanying table the names of the great divisions 

 of existing insects that have not been satisfactorily connected by 

 morphological and ontogenetic stud)- are placed in a consecutive 

 arrangement, and are grouped in accordance with our present 

 knowledge under four heads, Apterygota, Anapterygota, Exoptery- 

 gota, Endopterygota : these four groups represent generalisations 

 as regards the development of the wings. 



The Apterygota include the two orders Thysanura and Collem- 

 bola. These insects are quite wingless, and are usually considered 

 to be the descendants of a stock never having possessed wings. 



The Apterygota exhibit, so far as is known, but little or no 

 metamorphosis during the postembryonic period. 



The Anapterygota consist of wingless forms that are supposed 

 to be descended from winged forms. They are all parasitic on 

 vertebrates during the whole or part of their lives. The evidence 



