280 MICROSCOPY FOR BEGINNERS. 



jects, unless the student is sufficiently expert to be able 

 to remove the pigment matter and so make them trans- 

 parent. This can be done with moderate ease in the 

 large compound eyes of the house-fly, but with most 

 other insects it is a delicate operation. The eyes are re- 

 moved with sharp scissors, soaked in solution of caustic 

 potash, and the pigment washed from the inside, if nec- 

 essary, with a fine wet camel's-hair brush. The work is 

 best done under water, and the cleaned eye may then be 

 examined in water. The compound eyes of insects like 

 the house-fly are usually so large and convex that only a 

 small part of the surface can be brought into focus at 

 the same time ; they are often sufficiently transparent 

 to be quite easily studied without the troublesome 

 cleaning process. The facets of compound eyes often 

 have long hairs between them. The eyes of spiders are 

 several, and are arranged on the top of the head. If the 

 spider is small, place the whole body under a low power, 

 and view as an opaque object ; otherwise cut into parts 

 to suit. The eyes have a wicked look as they brightly 

 gleam in the reflected light. 



5. PKOBOSCES OF INSECTS are as numerous and varied in 

 structure as the insects. They should be cut off close to 

 the body, squeezing the insect to force out the parts if 

 necessary. Examine in water or glycerine, covering them 

 with a thin glass square or circle as already explained. 

 The tongue or proboscis of a butterfly is interesting. 

 The latter is usually quite visible as a small coil just 

 under the front of the head. It may be unrolled with 



