98 MOSQUITOES OF NORTH AMERICA 



suture. This suture extends posteriorly in two branches from the bases of the 

 antennae, the two branches uniting behind a short distance before the foramen ; 

 from this point backwards it forms a single median suture. It is along these 

 lines that the head splits open and in continuation a rent appears along the 

 median line of the thorax. The head moult remains attached to the skin of the 

 body. 



The last moult, or transformation to pupa, is described by Hurst as follows : 

 " Towards the end of larval life the animal becomes sluggish ; profound changes 

 in its mouth-parts deprive it of the power of eating, and it floats with its siphon- 

 stigma at the surface. Shortly the cuticle bursts in the thoracic region, along 

 the mid-dorsal line ; the pupal ' horns ' or siphons are protruded, the abdominal 

 trachea appear to collapse, and the animal floats with the anterior end up- 

 wards, the new siphons coming to the surface. The old larval siphon, or rather 

 its soft parts, are withdrawn from the cuticle and invaginated into the eighth 

 segment of the abdomen; the intima of the abdominal and thoracic tracheal 

 trunks beak up into pieces, which in the abdomen correspond to body-segments. 

 The body of the escaping pupa is gradually withdrawn from the larval cuticle, 

 and the eighteen fragments of the old tracheal intima are drawn out of the body 

 by nine pairs of stigmata, and cast off with the exuvia. These nine pairs of 

 stigmata are situated, one in the hinder part of the thorax, one in each of the 

 first seven segments of the abdomen, and the ninth pair are united to form a 

 single aperture, the old respiratory opening at the end of the larval siphon." 



