Page:A note on grappling tail-hooks in anopheline larvae - M.O.T. Iyengar - 1922.pdf/6

Rh placed. Frequently, the two tufts may cross each other (Plate LXI, fig. 1. A). It will be seen from Plate LXI, fig. 4, that there are many more branches on the dorsal than on the ventral side. In A. hyrcanus there are 12 dorsal and only 4 ventral branches, and in some cases the ventral branches are still fewer.

The outer tufts consist each of about six equally long strongly chitinised setæ the tips of which are bent and sharply hooked and a few (2 to 4 or more) thin branches ventrally which possess no hooks. In some forms, the number of such hooked setæ may be as many as 7—10. The branches are somewhat flat at their bases. The hooks on the external supra-anal setæ are strong and thick. But the branches of the median supra-anal tufts have also been found in a few cases to have very minute hooks at their tips, visible only under the high power. They are very small and feeble, and may not be of any great use. I have found them in the larvæ of A. maculipalpis, culicifacies and minimus.

The following are observations of larvæ of Anopheles stephensi breeding in cisterns in Calcutta. When the larva rests along the surface of the water, the hooked setæ are projected backwards and the hooks point downwards (Plates, LXI and LXII, figs. 4-5). When disturbed, the larva goes to the bottom if the water is shallow. But if deeper, it has been observed to go only to the side of the cistern and sink slowly with the tail end touching the side. While thus descending, the hooks catch even the smallest prominence or roughness in the side and the larva hangs head downwards from the wall of the cistern by means of these hooks. It sticks to this position as long as the disturbance continues, and when everything is quiet again comes up to the surface. If from one such resting position the larva is disturbed by touching it gently with a long needle, it either comes up to the surface, or more frequently goes to another place on the cistern side and hangs from the new position in the same way. This led me to suspect the presence of some grappling organs in the tail, and an examination showed that these were the hooks of the external supra-anal tufts. Larvæ can stick to the sides of even a glass-jar in which they may be kept and dangle head downwards for varying lengths of time. In one instance, a larva clung to the sides of a cistern, under water for as long as 3 minutes.

All the species of Anopheles available for study have been examined since, including A. subpictus, Grassi (grossi, Giles); vagus Donitz; culicifacies, Giles; fuliginosus, Giles; jamesi, Theob; maculipalpis,