94 W. A. LAMBORN. 



attenuated as in Cidex and often crooked, and show hooks so diminutive as to make 

 the determination of their presence difficult. In this also the upper of the dorsal tufts 

 is reduced to a mere bristle clothed with a few sparse hairs. 



It was of interest to learn from Col. Alcock, of the London School of Tropical 

 Medicine, that these structures are present also in two of the British species, and that 

 in the third, breeding in situations comparable with those favoured by A . asiaticus 

 in the Federated Malay States, they are, as in that species, absent. The paragraph in 

 his letter, dated 10th August 1920, which he has kindly allowed me to quote, is as 

 follows : — 



" On looking at the larvae of the three British species (after reading your letter), 

 I find it to be as you describe in A. niaculipennis and in .4. bifurcatus, but not in A. 

 plumbcHs, that breeds in holes of trees. Now I understand how the larvae of the former 

 two species anchor themselves at right angles to the sides of the aquarium." 



Were these structures used for swimming, one would expect to find them at their 

 maximum development in larvae which move more actively than most Anophelines 

 in search of food, but this is not the case. Stegomyia probably owe their success as 

 a race of mosquitos, not merely to their being able to breed in almost any situation 

 invariably in stagnant water in which insect enemies are commonly absent, but to the 

 activity they are able to develop in their search, both at the surface and at a depth, 

 for the scanty and miscellaneous food material such places often afford. Placed in 

 a bowl, they may be seen moving constantly, head down, over any surface on which 

 food material may be obtained ; they never remain passive at the side, content to 

 take such food as comes along, as some Anopheline larvae do. In these larvae the 

 various caudal structures are least developed, being represented by a much simpler 

 arrangement of hairs. There are in the last ecdysis three dorsal and three ventral 

 hairs only on each side, all relatively longer than in Anophelines (except in A . asiaticus) , 

 perfectly straight and tapering gradually so as to end in a fine needle-point. 



Anopheles larvae may be called on at times to make a sudden and very rapid 

 movement ; this is essential to enable them to escape their enemies, and it is effected 

 by all these larvae, which swim backwards, at all events when on the surface of the 

 water, by sudden contractions of the body, as in the case of Stegomyia. But it is 

 essential for such as live in moving water that the movements should be to some extent 

 objective, towards some support, so that they may avoid being swept away. It is 

 suggested that direction is attained by means of rudder-like action of the ventral 

 fans, also much more highly developed than in Stegomyia, which, furthermore, enable 

 them on occasion to turn sharply so as to attach themselves to any support by means 

 of the hooks of the dorsal brushes, which have just been described. 



The function of the hooks was very readily determined by affording larvae in a glass 

 dish, a small twig as a rough object of support. The larvae of all species except 

 A. asiaticus, especially those commonly found in moving water — A. niaculatus and 

 A. kan&ari for instance — invariably take advantage at once of such a support, 

 resting at a right angle to it. Even with the unaided eye, when the larva is at rest 

 against the support, it can be seen that the caudal tufts are so arranged that the ventral 

 group and the inner dorsal brush remain in direct line with the body, the latter just 

 touching the support, and that the dorsal leash of hooked filaments is directed out on 

 either side at an angle of about 45 degrees to the body. If the supporting object is 

 slightly submerged the brushes are directed down, obliquely or vertically, but still 

 occupy the same relative position. By the aid of a microscope it can be determined 

 that the booklets are twined round any rough point, so neatly sometimes as almost to 

 tempt one to suspect a real tendril-like action. 



If the supporting body is dragged through the water, larvae may be drawn along 

 still clinging to it, and the support may be rather violently moved to and fro, the 



