QUEKETT MICROSCOPICAL CLUB. 389 



aquatic, and in order to understand their life-history the surface 

 tension of water should be studied, as it was essential to the 

 life of the gnat, which in all its phases was an air breather. The 

 eggs were laid in the form of a floating raft, about a quarter of 

 an inch in length, containing some 250 ; they were cigar-shaped, 

 pointed above and with a lid below, from which the larvae emerged. 

 The larva was heavier than water, yet required to breathe the 

 air; for this purpose a posterior breathing-tube, known as the 

 respiratory siphon, arose from the eighth abdominal segment, 

 and at the end was armed with five cusps, which, when expanded, 

 supported the creature tail upwards, by virtue of the surface 

 tension ; its head meanwhile sinking in the water, from which its 

 food was obtained. When alarmed it withdrew the cusps and 

 was able to progress by using the swimmerets at the end of the 

 body. After three or four months it pupated and the pupa did 

 not feed, but it was requisite that the head should be towards the 

 surface for the emergence of the perfect insect. To accomplish 

 this, two trumpet-shaped breathing-tubes were developed from 

 the back of the head, and these, owing to the surface tension, were 

 able to support the creature in the new position. Finally, the 

 pupa-case split along the back, and the gnat, withdrawing from it, 

 began its new life in the air. In reply to questions. Dr. Leeson said 

 the blood-sucking function was not well understood. Swarms 

 of gnats inhabited the Arctic regions where no animals existed 

 from which a supply could be drawn, so that the propensity could 

 hardly be considered essential to its existence. As the males did 

 not suck blood, it might, perhaps, be an accompaniment of the 

 reproductive function. The danger of contracting malaria from 

 the bite depended on the presence of infected people in the area 

 from whom the parasite might be transferred. Mr. N. E. Brown 

 referred to the dissemination of ague by Culex 'pipiens, and Mr. 

 Grundy remarked that ague in India was almost certain to follow 

 the bites of various gnats. After some observations by the chair- 

 man, a hearty vote of thanks was accorded to Dr. Leeson for his 

 communication. 



Mr. Jas. Grundy, F.R.M.S., explained the polarising apparatus 

 given with the microscope by Mr. Ingpen. The theory of polarised 

 light, and the differences between plane, elliptical and circular 

 polarisation, were referred to. It was shown how rays of light 

 passing through the polariser were divided up into ordinary and 



