54 





Owing to the small si/.c of tlu ts, the majority of them 



.pe the attention of all ' the more Careful student 



nature. Ti: t to entom* 



for it in. ' or simplest of the true in :ul in it 



which >ho\v close affinities to the next lower cl 



the My: It is thus one of the connecting links of which we 



r so much in these days; and in it are, doubtless, forms which 



einblc than any other living species those \\hich in 



.cal times were the first llexapoda to appe.ir on the 



earth. 



The low rank of these insects is indicated in many ways. The 

 .til-parts are of a primitive form; wings are never developed; 

 the insects undergo no metamorphosis, the larval form b< 

 retained by the adult. 



:ice of wings in this order is believed to represent the primitive con- 



;i of these insects. None of the species show any indication of the <ii 



opnient of these or \nd the thorax does not present that complication 



iiicture which is the result of the development of wing-muscles. In each 



of the higher orders we find wingless species; but in these cases there is good 



r believing that the wingless condition is the result of a retiv, grade 



lopment. In -es this degradation is the result of parasitic habits, 



th lice, fleas, and mady other parasites; in other instances it is the result 



of the separation of the species into several castes, of which some do not re- 



quip- a the workers and soldiers among Termes, and the sedentary 



generations of the Aphides. 



Upon the distinction given above Professor Brauer separates the insects into 

 Tlie first includes only the Thysanura ; this he calls the Aj\ 

 gogcnea, or "originally wingless inse 

 it coincides with the super-order Symip- 

 /<><!<){ Packard. The second cla-s liiauer 

 terms tin- /': r " originally 



winged insects." 



The form of the mouth-parts of 

 the Thysanura is very different from 

 that seen elsewhere in the class 

 .. . Ilrxapoda. Here the- mandibles 



uT i) / ^P6~ an(I maxill;L> - iitiiougii r ' tu ' (l f " r hit - 

 Tr tractcd within the head, 



instead of being attached externally 



with tin- higher in- 

 ts whose- mouth-parts an- formed 

 I. -hows the relation of the jaws to the wall of 

 1 in a common .spring-tail, one of the ILntomobryidic. In this 





-'.**; 



MMible; ii. maxill.*; 12, labitim; i.-</. la- 



