MORPHOLOGICAL CHANGES OF STEGOMYIA FASCIATA. 



299 



The antennal plume is much reduced. In the earliest phase it is represented by a 

 double sub-plumose hair, but in the three later phases by a single short simple hair ; 

 very occasionally a double hair may be present in the second phase. The position of 

 this plume is somewhat variable, and is not always the same on the two sides of the 

 head. In the first phase it was situated at 2 or, more usually, 3 units from the base 

 of the antenna, in the second phase 4 or 5 units, in the third phase 6 to 8 but usually 

 7 units, and in the last phase 10 to 14 units. That is, as the larva develops the position 

 of the plume shifts slightly from just below to a little above the middle point. 



The shaft of the antenna bears a considerable number of minute spines in the 

 earliest larval stages, but these are very few in the third phase, and are apparently 

 completely absent in the last phase. 



Eyes (fig. 1). The eyes were small and rounded in all the larvae examined. Their 

 approximate diameter was 1| units in the first phase, 3 or a little more in the second, 

 3 to 4 in the third, and 4 to 5 in the fourth. In the youngest larvae they could some- 

 times be seen to be made up of several pieces, generally three. In the fourth phase a 

 rather less dense patch of pigment lay like an eyebrow in front of the darker and 

 denser circular patch of the eye ; this was the so-called " main " eye, the organ which 

 is said to become the compound eye of the imago. 



Fig. 2. Labial plate of the larva of Stegomyia fasciata in the four stages. 



Labial Plate (fig. 2). The number of teeth on each side of the large median tooth 

 of the labial plate showed slight individual variations, but much greater developmental 

 changes. In the first phase there were 7 or 8 teeth, in the second 9 or 10, in the third 

 10 to 12, and in the fourth 13 to 14. In the later stages the labial plate was much 

 more highly chitinised than in the earlier, but in each phase it conformed to the tj'pical 

 plan, a triangular body with a large median tooth at the apex, and smaller teeth down 

 each side, those nearest the median tooth being smaller and more closely set than 

 those further away. 



Thorax. The thorax is at first very small, but increases rapidly in size and in 

 proportion to the other parts of the body as the larva matures. In the first phase 

 the diameter of the thorax is less than or about the same as that of the head, namely, 

 about 10 to 13 units. In the second phase the thorax and head are about equally 

 broad, but by the time the third phase is reached the thorax is definitely the broader, 

 the ratio in one larva being for example 53 : 42, and in the fourth phase it is broader 

 still, the ratios in two larvae being 75 : 55, and 90 : 55 respectively. The breadth of 

 the thorax is a conspicuous feature of the mature larva. 



