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ON THE OCCURRENCE OF THE IMMATURE 

 STAGES OF ANOPHELES IN LONDON. 



By FLORENCE E. JARVIS. 



The observations recorded below were made between September 1917 

 and September 1918. The area selected was approximately a circle with 

 its centre at Charing Cross and a radins of about nine miles. The majority 

 of the pieces of water examined were ornamental ponds in the various 

 London parks, but in addition a number of natural ponds, swamps, and 

 ditches were searched. 



Positive results for Anopheles maculi'pennis were obtained from six- 

 teen out of a total number of thirty-seven pieces of water investigated. 

 A. bifurcatus occurred in one locality; A. phimbeus {— nigripes) was not 

 observed. 



During the spring and early summer of 1918 the presence of immature 

 stages of A. maculipemiis was noted in or near the outer limit of the 

 selected area only. Later in the season, in August, considerable numbers 

 of larvae were obtained from places much nearer the centre of the circle, 

 e.g. Chelsea Physic Garden and Battersea Park. These facts seem to 

 suggest the possible occurrence during the summer of an inward migra- 

 tion of adults from more outlying suburbs. The two places mentioned 

 above lie opposite one another on the north and south sides of the Thames 

 respectively and are enclosed by houses on three sides, the fourth side 

 being open to the river, A migration of adults to Chelsea and Battersea 

 could thus conceivably take place along the course of the river from the 

 marshy districts lying near the mouth. The west and south-west winds 

 however, which prevailed during the greater part of the summer of 1918, 

 would appear to have been able to hinder effectively a migration in this 

 direction. A visit made in September to an ornamental pond in Staple 

 Inn yielded a negative result which could be attributed (1) to the densely- 

 populated nature of the locality, and (2) to the presence of a number of 

 gold-fish in the water. 



In the accompanying table are given, in order of date, the pieces of 

 water visited. Many of these proved unsuitable for breeding places, 

 while in certain other cases conditions were apparently favourable but 



