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used under this lens. It may be 16 in. long, 4 in. high, and 4 or 5 in. broad.

Various kinds of dissecting microscopes are on the market, and these are to be recommended when they can be afforded.

A.—

B.— 1/2 natural size.

C.—

D.—

Instructions for the use of the compound microscope, with which some schools may be equipped, cannot be given in a brief space; the technique requires careful training. Such microscopes are not needed unless the pupil studies cells and tissues.