THORAX OF WINGED INSECTS. 467 



the operation of flying. Again, it is contrary to analogy to 

 consider this segment as " le premier segment abdominal," from 

 the appendages attached to it; and which, taking into consider- 

 ation the various forms adopted by other thoracic appendages, 

 and the want of any such analogous movable appendages 

 attached to the abdominal segments of other insects, must be 

 regarded as thoracic. Moreover, as to the circumstance that this 

 " premier segment abdominal " is furnished with spiracles, 

 (which, were it the raetathorax, as is stated, it ought not to 

 possess,) I cannot but think that much too great a stress has 

 been laid upon it; the situation of the respiratory organs 

 being very variable in different groups : thus, in the Lihellula 

 and Cimex there is a pair of metathoracic spiracles, whilst in 

 the Apterous PJiasmidcs the metathorax is said to have four. 

 {See Latr. Cours d'Ent. 185; and Kirby and Spence, iv. 43.) 



Notwithstanding the incorrect view (as it appears to me) 

 which Latreille has taken of the structure of the hinder part of 

 the thorax, he adopted the general opinion, that the con- 

 spicuous piece which followed the large thoracic shield was 

 the representative of the true scutellum of the mesothorax.® 

 Messrs. Kirby and Spence, however, observing that the meso- 

 thoracic scutellum of the Hymenoptera is connected at the sides 

 with the base of the upper wings, considered that in the Diptera 

 *' the part that has been usually called the scutellum is not at 

 all connected, either by situation or as a point of attachment, 

 with the wing itself, but with the lower valve of the alula, 

 which is with reason thought to be the representative of the 

 secondary wing of the tetrapterous orders." (Vol. iii. p. 559.) 



The Dipterous mesothoracic scutellum is supposed by these 

 authors to be represented by *' the bilobed piece situated be- 

 tween the wings, and to the side of which they are attached ;" 

 and they regard the halteres as additional metathoracic ap- 

 pendages. If, indeed, the alulas represented the lower wings, 

 the view which Messrs. Kirby and Spence take, relative to the 

 scutellum, would doubtless be correct ; but from what has been 

 already advanced, I think we are warranted in considering the 



« If Latreille be correct in regarding the alulae as lower wings, he is at least 

 incorrect in applying the term mesothoracic scutellum to the hinder conspicuous 

 piece of the Dipterous thorax, which, as Messrs. Kirby and Spence well observe, 

 is connected with the base of the alulae, and would, in such case, necessarily be a 

 metathoracic piece. 



