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MORPHOLOGICAL CHANGES OBSERVED DURING THE DEVELOPMENT 

 OF THE LARVA OF STEGOMYIA FASCIATA. 



By J. W. Scott Macfie, M.A., 



West African Medical Staff. 



The larva of Stegomyia fasciata passes through four distinct phases after it emerges 

 from the egg and before it pupates. Under circumstances favourable to growth these 

 phases are passed through very rapidly and the whole larval stage may occupy less 

 than a week. In one experiment ten larvae which had hatched from their eggs on 

 1st April between 12 noon and 2 p.m. were isolated singly in small glass tubes con- 

 taining a three-days-old broth medium. All these larvae cast their first pelts on the 

 second day (2nd April), their second pelts on the third day, and their third pelts on 

 the fourth day. The fourth and last larval pelt was not cast simultaneously by all 

 the larvae, perhaps because by this time the nutrient value of the medium in the 

 different tubes had begun to vary to an appreciable degree. Two larvae cast the 

 fourth pelt on the seventh day, one on the eighth day, three on the ninth, one on the 

 tenth, and one on the thirteenth day, and two died in this phase. One pupa died, but 

 all the others hatched on the second day after pupation. In this experiment therefore 

 the larval stage lasted on the average nine days, the shortest time being under seven 

 days, and the longest thirteen days.* 



In the intervals between their moults mosquito larvae do not appear to undergo 

 external morphological changes. Certain structures do become more highly 

 chitinised in these periods, but speaking generally, the structure remains constant 

 during each phase. In the course of development, however, the larvae of Stegomyia 

 fasciata undergo marked morphological changes, and these can be followed in the 

 case of individuals by an examination of the four pelts cast by each. This has been 

 done in the case of the larvae used in the experiment mentioned above. The obser- 

 vations have been confirmed and extended by the examination of living larvae and 

 of larvae killed and preserved at each of the four stages into which the larval period 

 is divided. This was necessary, as it is not possible to measure, for example, the 

 thoracic diameter or the length of the siphon of a young larva in the pelt, since these 

 parts become distorted. 



In the descriptions that follow the structures that show definite changes during 

 the larval periods will be dealt with one by one, and subsequently the characteristics 

 of each of the larval phases will be summarised. The unit employed in making the 

 measurements was approximately 16/t (50 units = 0-8 mm.). 



* The eggs had been laid on 30th March, so that the period from the time the eggs were 

 laid to the time whon tlie adult mosqiiitos emerged ranged from 11 to 17 days and averaged 

 13 days. 



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