37 



Insecta stand apart from the Arachnida and all other Arthropods l , 

 whilst two singular animals — the Peripatus and Scolopendrella — ■ 

 appear to connect the insects with the Annelids. The peculiar 

 structure of these animals suggests them as stranded surviving 

 remnants of a multitude of extinct forms, leading up from ancestors, 

 at least closely allied to the Annelid worms, to insects. 



The relation of insects to each other has formed the basis of much 

 exact and detailed study ; and it is probably the amount of detailed 

 observation made that has led to so much diversity of opinion among 

 specialists, one considering certain characters of importance that are 

 not supposed to be of much value by others. Generally speaking, 

 however, the nature of the metamorphosis has formed the broad 

 basis on which most systems of classification have been founded ; 

 and so long as one recognises that the character of the metamorphosis 

 represents the degree of specialisation of the various classes of Insecta, 

 the arrangement based thereon must be considered a fairly safe one. 

 On this basis we have two main divisions, the first comprising two 

 classes whose species are without wings and ametabolous, i. e. not 

 presenting any of the ordinary phenomena of metamorphosis. 



The second includes the winged forms ; but since the degree of 

 metamorphosis which the latter undergo varies considerably, this 

 section is subdivided into the heterometabolous and holometabolous 

 groups, — the former including those orders that have a more or less 

 incomplete, the latter those orders that have a complete metamor- 

 phosis. These may be tabulated thus : 



r 



Insecta <j 



Synaptera 



■••{i 



f Heterometabola ■{ 



[_ Pterygota « 



t^ Holometabola 



Thysanura. 



Colembola. 



Orthoptera. 



Dermaptera. 



Platyptera. 



Ephemeridae. 



Odonata. 



Thysanoptera. 



Hemiptera. 

 f i. Trichoptera. 

 | 2. Lepidoptera. 

 <{ 3. Diptera. 

 j 4. Hymenoptera. 

 [__ 5. Coleoptera. 



Since, however, as we have stated, this system of classification is 

 based on the phenomena presented by metamorphosis, and we 

 propose dealing later with this subject, we may leave the considera- 

 tion of the relationship existing between the heterometabola and 

 holometabola until later in the paper. 



It would be impossible even to give the barest outline or indication 

 of the biological work that has been done in relation to insects. 

 When we consider the various stages through which insects pass, 

 the complexity of almost every tissue and organ, and remember that 

 every tissue and every organ has been, perhaps, the life-study of 



