52 MICROSCOPIC ILLUSTRATIONS. 



These must then be carefully examined by removing 

 small quantities at a time into a white saucer, or small 

 wide-mouthed phial. When they have been examined in 

 this vessel with a hand-magnifier, the objects sought for 

 should be removed to a store-jar, and the refuse thrown 

 away ; then inspect another portion, as before, until 

 all the water taken at a draught has undergone 

 examination. 



Although nearly a quarter of an inch long in its 

 nascent state, this larva can scarcely be observed without 

 a hand-magnifier of about two or three inches focus 

 (unless the collector be short-sighted), as all its parts are 

 nearly colourless, except two pairs of kidney shaped 

 bodies, which have a metallic appearance, and are nearly 

 opaque, as shewn in the plate at b, and d, in the mag- 

 nified side view, fig. 1. 



The drawing, fig. 1, represents the creature in the 

 larva state. Fig. 2, shews the same being a day after- 

 wards, when it had changed to the pupa state. On com- 

 paring the two drawings, however, a very remarkable 

 and complete change of structure throughout will be 

 clearly perceived. 



In the larva, fig. 1, the obvious and curious parts are 

 the kidney-shaped bodies b, and d, two of which are 

 situated near the head, and the other two in the third 

 division from the lower extremity. The first pair are 

 inclined towards each other, while the others lie in pa- 

 rallel planes, as represented in the plan, or bird's-eye 

 view, drawn of the natural size in fig. 3. Physiologists 

 have not ascertained what may be the functions performed 



