ABSTRACT
The processes of osmotic regulation in the larvae of Aedes aegypti and of A. detritus have been studied by determination of the freezing-point of samples of fluid collected from different parts of the gut.
In A. aegypti, kept in fresh water (its normal environment), the fluid passing down the intestine to the rectum is isotonic with the haemolymph. In the rectum it becomes strongly hypotonic before being eliminated.
In A. detritus, kept in sea water (its normal environment), the opposite process is observed, the fluid in the rectum becoming hypertonic to the haemolymph and approximately isotonic with the external medium before being eliminated.
In A. detritus, which is able to live in dilute media as well as in sea water, the only two specimens from fresh water available for examination were found to have the rectal fluid hypotonic to the haemolymph.
The ability of A. detritus, not possessed by A. aegypti, to produce an hyper-tonic fluid in the rectum is tentatively associated with a region in the anterior part of the rectum and lined with an epithelium distinctly different from that in the remainder of the rectum. This anterior region has not been found in A. aegypti.
It is quite simple to prepare in the following way a small (100μ diameter) cannula with a flared end which retains a ligature. Pyrex tubing is used, and is first drawn down to the required diameter and taper. The tapering point is broken off to the required length and is sealed off by being held in the edge of a coal-gas microflame (about 1 · 5 mm. height). The fine tube is then withdrawn from the flame and is connected to a compressed air supply at about one atmosphere pressure. The sealed end is again very carefully introduced into the edge of the flame. As it fuses a bubble forms and bursts. The remaras of the bubble are broken off with fine forceps, leaving a jagged flared end. This end is then brought up to the edge of the flame (or to a nichrome wire heated bright red) and the jagged edges are allowed to round off. For these operations a binocular of medium power is desirable.
In view of the errors inherent in the use of indicators for pH work the figures should not be taken to represent the true pH of the gut contents. The figures are intended to describe the colour of the indicator as it would appear in standard buffer solutions.
