^ w. weschl^. the larval and 



Technique of Examination. 



The larvae and pupae were preserved in tubes of formalin ; it was desirable 

 that they should be examined in the medium they had been in, so they were 

 taken out of the tubes by a small lifter * and transferred to a shallow glass 

 trough, half full of formalin ; this was placed on the stage (flat) of the 

 compound microscope, and the larvse examined with a magnification of about 

 60 diameters. In those with very long siphons, and in all the pupae, some 

 difficulty will be met with in getting dorsal views, and even more difficulty 

 in getting ventral views. In the larvae, when material is abundant, this is 

 got over by detaching the head, or the siphon. In cases where it is not 

 •desirable to damage the specimens, and with the pupa?, the difficulty can be 

 got over by using a rectangular trough with sides about 2 mm. deep, when 

 the head or the upright siphon can be placed in the angles f. 



In manipulation it is well to use a bristle in a handle, or, better still, the 

 finest entomological pin with the head off, and fixed in a handle till only 

 4 mm. remains visible ; the point must be pared down (on a glass slip is 

 best) with a penknife, till only a fine strip of metal remains, and the last half 

 millimetre is slightly bent. 



A dorsal examination gives the best view of the antennae and of the facial 

 plumes and eyes, but the ventral side shows the mouth better. To under- 

 stand the mouth structures properly, they must be carefully dissected and 

 teased apart ; the fragments cleared in phenol and xylol, spread on a glass 

 slip, and mounted in balsam. 



The thorax and abdomen must be looked at from both sides. The weight 

 of the siphon will, except in the case of the Anopheline larvae, or in those 

 with very short siphons, turn the last two segments of the abdomen partially 

 round, so that a lateral view, or semi-lateral view, is obtained of the seventh 

 segment. If there is any difficulty, wedge the head in a corner. 



The siphon, comb and anal segment are best seen laterally, except in the 

 case of very dark larvae ; the pupae are also to be examined in this way ; but 

 when the anal plates are looked at, a dorsal or ventral view is necessary, and 

 then the creature has the last three segments broken off, or is placed on its 

 back with its head in a corner, or is hung on a bent pin, as suggested in the 

 note below. 



Measurements and Comparisons. 



Thes(i are best made with a numbered scale dropped in the eyepiece of the 

 microscope, when the units can be read off and compared. 



* A strip of zinc 2 mm. broad, and of suitable length, fixed in a handle, answers well. 



t A much bent mosquito pin (silver and as thin as possible) shaped so that it forms a cradle 

 or a little elevation, can be placed in the trough, and the larvae and pupae arranged on it, so 

 as to give particular angles ; this has been found very useful. 



