THE PUPAL STAGE OF CULEX. 49 



All these eight pairs alike arise as foldings of the epidermis 

 (" hypodermis ") outwards. All alike are completely hidden by the 

 larval cuticle. 



The antenna?, moreover, are much larger in an advanced larva 

 than they appear to be. Their growth forwards being prevented by 

 the unyielding cuticle, they grow backwards, and their basal portion 

 is folded, and even " telescoped." 



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 tracheae 

 appear to collapse, and the animal floats with the anterior end 

 upwards, 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 siphon, or rather its soft parts, are withdrawn from the cuticle and 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 breaks 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 the escaping pupa is gradually withdrawn from the larval cuticle, and 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 exuviae. 

 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. 



With the larval exuviae are also cast off the cuticular portions 

 of the jaws and antennae, and all the hairs and spines with which 

 the larval cuticle was beset. 



The pupa which thus escapes differs from the larva very widely. 

 It is a little under 1 cm. in length when fully extended. It consists 

 of a bulky, laterally compressed mass made up of head and thorax 

 with their appendages, and of a slender flexible abdomen, which 

 when at rest is curved under the thorax. In a specimen measuring 

 9 mm., which is nearly the maximum size, the thorax measures 

 2*5 mm. and the abdomen 6-5 mm., but the thorax appears to be 

 much longer on account of the wings which extend downwards and 

 backwards from its sides. 



The head lies below the thorax, and so adds nothing to the length 

 E 



