Vol. 1.1 Wood wort li. — W lug Veins of htsects. 21 



In the Odonata and P]phenierida^ there is no deep infolding 

 for muscle attachment, but the external appearance is not ver}^ 

 different, the additional pieces evidently resulting from the 

 need of a firmer attachment for the parts that vibrate with 

 the wings and in the perfection of the anterior and posterior 

 notal articulation. The pra^scutum of the mesothorax and 

 the back of the first abdominal segment are especially devel- 

 oped to strengthen the thorax, because the remainder of the 

 mesonotum and the whole of the metanotum are loose and 

 beat with the wing. 



As a resvyne, we may recall that the position of the wing 

 on the segment, though subject to some variation, always 

 marks the division between dorsum and pleuron, but there 

 is difference of opinion as to the exact relation of these parts. 

 The theories of composite segments in the thorax seem to be 

 entirely untenable and would not throw light on the question, 

 if true. The real solution requires a study of the specialization 

 of the thoracic segment, and must include the consideration of 

 thoracic functions. Two distinct types of sclerite division may 

 be distinguished, one for articulation, the other for resistance; 

 both of these occur in the thorax, but the latter only causes the 

 separation of the principal sclerites. The first stage in thoracic 

 specialization follows the development of the legs, and results 

 in the separation of the sternum from the remainder of the 

 segment and the beginning of the division which ultimately 

 separates the episternum from the epimeron and the scutum 

 from the scutellum. The completion of this division, the 

 separation of the dorsal from the pleural region, and the 

 development of the pra'scutum and of the postscutellum, mark 

 the final stage, which is brought al)Out by the development of 

 the wings, and tlie wings can not, therefore, be considered as 

 a product of either the pleuron or the notum, but rather as the 

 means of their differentiation phylogenetically as well as 

 ontogenetically. 



FLIGHT. 



The one fact in regard to which all authors who have written 

 on the subject of fiight in insects are in agreement, is, that 

 insect flight is not comparable with the flight of birds. The 

 path over which the wing of an insect moves in flight is shaped 

 like the figure 8, contrasting sharply with the oval path of a 

 bird's wing. Furthermore, it is to be noted that while the 



