MORPHOLOGICAL CHANGES OF STEGOMYIA FASCIATA. 305 



times reaching 13 (5, 2 ; 5, 1) and sometimes being as few as 9 (3, 2 ; 3, 1) ; but 

 although there is no reason to suppose that these are the limits of variability, it-should 

 be stated that in none of the larvae examined at this stage did the number fall as low 

 as that found during the third phase, namely 6 (2, 1 ; 2, 1). In proportion to the 

 size of the larva the hairs are very much longer in the first phase than they are later. 



These then were the more important morphological changes observed to occur 

 during the development of the larva of Stegomyia fasciata. Some previous descrip- 

 tions, as for example that of Wesche, would appear to have been pieced together 

 from observations made on larvae of different ages, and for this reason it may be as 

 well to summarise the more prominent features characteristic of the larva at each of 

 the four phases of its development. 



First Phase. 



During the first phase the larva is a minute whitish body. The antenna is 7 units 

 long, and bears in place of a plume a double sub-plumose hair at a point just below 

 the middle ; the shaft is studded with minute spines. The labial plate has 7 or 8 

 teeth on each side. The thorax is narrower than or about the same width as the head, 

 and the two pairs of ventral hooks are quite rudimentary. The comb consists of 

 4 to 6 scales. The length of the siphon is rather more than twice its basal diameter, 

 and the hair-tuft, a, single simple hair, is situated a little beyond the middle ; only 

 the extreme tip of the siphon is chitinised. The pecten is composed of 4 or 5 scales. 

 The anal segment is slightly longer than broad, and a saddle-shaped dorsal patch is 

 chitinised. The anal papillae are slightly longer than the anal segment. There are 

 four simple hairs on the dorsal edge of the anal segment, but no ventral hairs or 

 beard. 



Second Phase. 



In the second phase the antenna is a little longer, about 9 un.its, and the plume, 

 which is close to the mid-point, is reduced to a single simple hair ; there are some little 

 h^pines on the antenna, but fewer than there are in the first phase. The labial plate 

 has 9 or 10 teeth on each side. The thorax is about the same width as the head and 

 tlie thoracic hooks are better developed. The comb comprises 8 to 10 scales. The 

 siphon is a little more than twice as long as broad, its tuft a double or triple hair, and 

 its end rather more extensively chitinised. The pecten is made up of 8 to 10 scales. 

 The anal segment is about as long as it is broad, and is rather more highly chitinised. 

 The papillae are less than twice as long as the anal segment. The dorsal hairs on the 

 anal segment are still simple, but there are now some ventral hairs and a rudimentary 

 beard. 



Third Phase. 



At this stage the larva is both darker in colour and more highly chitinised. The 

 antenna remains much the same but is longer, 13 to 14 units, and there are very few 

 spines on the shaft. The labial plate has 10 to 12 teeth on each side. The thorax is 

 considerably broader than the head, the ventral thoracic hooks being well developed. 

 The comb has about the same number of elements as in the second phase, but the 

 scales are more highly developed. The siphon is about twice as long as broad, and 



(C325) H 



