70(5 J\Ir. T. If. Taylor on 



luentioned. Of the remaining three branches, two have tlie 

 same relations as the corresponding trachea? in the larva. 

 One supplies the sheath of the prothoracic leg ; the other 

 the head and fore part of the thorax. This last trachea 

 divides into four branches which may be numbered as in 

 the larva. The 1st is coimected by a commissure with the 

 corresponding trachea of the other side. The 2nd and 

 3rd branches of the same side are connected together as 

 in the larva. The last trunk leading from the spiracle- 

 chamber is met with in the pupa for the first time. It 

 runs dorsahvards, and after a short course divides into an 

 anterior and a posterior branch. Each of these breaks up 

 into a copious brush of fine tracheoki; which supply the 

 dorsal region of the thorax. From the posterior branch a 

 slender trachea descends to supply the wing-sheath. The 

 spiracle-chamber is put into communication with the pupal 

 gill by means of a stout tracheal trunk which may be 

 called the traelical extension (fig. 3, ex). 



The pupal gills of Simulium have been described by 

 Vogler and others. They are paired, and carried on the 

 fore part of the thorax. Each gill consists of a stem 

 (fig. 3) which is short and thick, and of two (;S'. latipes) or 

 four (^'. rej^tans) branches, each of which divides into two 

 long slender filaments. The stem projects forwards, and 

 the filaments of each side lie nearly in one vertical plane. 

 The filaments are transversely wrinkled, and taper gradu- 

 ally to a point. When viewed by refiected light under a 

 low power of the microscope, the gill has a silvery 

 appearance, but appears quite black and opaque when 

 seen by transmitted light. After the gill is treated 

 with caustic potash, transparent patches appear upon 

 the filaments when viewed by transmitted light. These 

 gradually enlarge and coalesce until the whole gill 

 ])ecomes transparent. The appearance of the gill is now 

 dull by refiected light, and transparent by transmitted 

 light. A similar result follows on the ti'catmont of 

 the gill with strong alcohol. By thus treating the gill 

 with potash and with alcohol we learn that the filament 

 is hollow, and that the wall is composed of a thick 

 chitinous cuticle which resists potash solution. The 

 chitinous cuticle is composed of two layers, a thin super- 

 ficial and a thick deep stratum (figs. 4 and 5, ss, ds). The 

 deoj) stratum is apparently quite homogeneous ; it is very 

 rel'ractive, and stains readily with eosiu and other dyes. 



