100 MOSQUITOES OF NORTH AMERICA 



" The pupa does not eat. It breathes air through the apertures at the ends 

 of its siphons. It floats, thorax uppermost, by virtue of a large air cavity lying 

 imder the hinder part of the thorax and the anterior part of the abdomen. This 

 cavity is bounded in front by the legs, at the sides by the wings, and below by the 

 mouth-parts. It extends up at each side of the first segment of the abdomen, 

 where it is covered by the halteres, and into this part of the cavity at each side 

 opens a large stigma, held open by the fairly well-developed cuticular lining 

 ('intima'), and guarded near its entrance by numerous spines. These two 

 stigmata belong to the first abdominal segment, and put the air-cavity just 

 described into direct communication with the tracheal system. As already men- 

 tioned, I regard this cavity and these stigmata as being mainly, if not ex- 

 clusively, hydrostatic in function, serving not only to make the pupa float when 

 at rest, but to make it float in a definite position, with the thorax uppermost and 

 the apertures of the siphons at the surface of the water." 



There is no special necessity for dealing here with the internal anatomy of the 

 pupa, as will be understood from the following statement by Hurst : 



" As to the anatomy of the pupa, it is only necessary now to state that at the 

 beginning of pupal life the internal arrangements are those of the larva ; at the 

 end of that period they are those of the imago." 



Hurst has given an excellent description of the external conditions in the pupa 

 of Culex, which we quote herewith. We must, however, call attention to one dis- 

 crepancy : The region called by him the " prothorax " is in reality the meso- 

 thorax. De Meijere, in an extensive paper on the anterior spiracles of dipterous 

 pupge, considers the anterior thoracic spiracles and their appendages as pro- 

 thoracic, which, of course, also involves the region in question. A careful ex- 

 amination of the external conditions leads us to differ. In dipterous larvae the 

 spiracles in question are prothoracic, in the imago they occupy a position which 

 can not be designated as such with certainty. Hurst's description of the pupa 

 of Culex is as follows : 



" The head is broad from side to side ; the epicranium has a Avell-marked 

 median groove ; the clypeus, broad above, is gradually narrowed below, and con- 

 tinued without any distinct line of demarcation into the labrum. At the sides 

 are a pair of compound eijes, to be regarded rather as the rudiments of the eyes 

 of the future gnat than as the visual organs of the pupa itself. . . . During 

 pupal life they increase in size till they almost encircle the head. Corneal facets 

 are never formed in the pupal cuticle, but beneath it the convex facets of the 

 imaginal cornea are formed during pupal life. 



" Behind the compound eye, on each side of the head, is an ocellus with fully- 

 developed lens, etc. In the youngest pupae it is separated by a small interval 

 from the compound eye ; but the growth of the latter obliterates this interval, 

 and the ocellus is in the older pupae not readily distinguishable except in sec- 

 tions. The statement, found in systematic works, that the Tipularise are devoid 

 of ocelli is, however, not strictly true; in Culex, at least, they are well developed, 

 though, as they abut upon the compound eye, they are in the imago so incon- 

 spicuous that they may easily be over-looked. 



" In the mouth-parts, the labrum, epipharynx, mandible, maxilla? with their 

 palps, labium and hypo- and epipharjmx are present, though the two last can 

 only be seen on dissection. 



" Of their mode of origin in the larva I as yet know nothing. At the time of 

 escape of the pupa from the larval cuticle they are of the full size, which is con- 



