158 7\*rco7'f]s of the Jndian Miisrinn. [Vol-. XV 



The spiracles, or the openings of the respiratory system of the larva 

 are two in number, one on each side, situated in a slight depression on 

 the dorsal surface of the eighth segment near the posterior margin of 

 its rectangular portion. The spiracles are surrounded by six chitinous 

 plates. When the larva is floating on the surface, the plates are spread 

 out (fig. 8), and expose the spiracles to the air ; when, however, the 

 larva goes down from the surface, the plates, as in the larva of Anopheles, 

 fold and with the fringes on their margins form a nearly closed cavity 

 over the spiracles, enclosing air, which prevents water from entering 

 the spiracles. The arrangement and shape of these plates is as follows : 

 Anteriorly there is a large transverse plate bearing seven or eight 

 groups of four to five setae each ; from its position and the attachment 

 of setae this thick plate appears capable of being turned over the spiracles, 

 which from their situation would then be drawn underneath it. Arising 

 behind the spiracle on each side is a chitinous plate of the shape of a 

 tennis-racket ; it is attached by the base of its handle ; the broader 

 portion, which stands free outside, is setose all along the margin. The 

 chitinous plates further behind consist of a large crescentic plate, broad 

 in the middle and drawn out along the two edges ; these drawn-out 

 portions are supported by the triangular plates with which the fins 

 articulate. 



This arrangement of the breathing mechanism of Dixa appears to be 

 homologous with that of Anopheles, only it is on a lower grade of 

 organization, all the essentials being the same. Both the mouth-parts 

 and the breathing apparatus of Anopheles can be very easily derived 

 from those of Dixa ; and the resemblances do not seem to be of the nature 

 of convergence, but rather to show a near relationship. 



Pupa of BiXA MONTANA. 



The pupa (fig. 13) is comma-like in appearance owing to the abdomen 

 being bent under the large cephalo-thoracic mass. It is of a dark 

 yellowish colour. 



The cephalo-thorax measures 2 mm. by 9 ram. The divisional lines 

 between the various abdominal segments are very well marked, and 

 there are well developed ridges on the abdominal segments ; there being 

 no hairs or setae anywhere. The opening of the breathing trumpets 

 is small, more or less squarish and lateral in position as usual. The 

 tail-fins (fig. 14) are peculiar in being very much reduced triangular 

 flaps, which are produced into a long regularly tapering spine a little 

 smaller than the fins. 



