ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



963 



Fig. 159. 



of the improvemeut consists in the employment of a truncated cone 

 of glass, in combination with one or more lenses capable of being 

 adjusted with respect to one 

 another. The conical surface 

 is highly polished, so as to 

 constitute an internally re- 

 flecting surface, the cone having 

 such an angle as to produce 

 total reflection. 



In fig. 159 A is the cone 

 mounted in a cell D and having 

 a lens B attached to its larger 

 end by transparent cement. C 

 is a second larger lens, and 

 mounted in suitable fittings E 

 and F, by which its distance 

 from B can be adjusted so as to 

 produce various effects. As improved efiects may in many instances 

 be produced by preventing the admission of light into the condenser 

 from one or other side of the lens C, a shutter G is added, pivoted 

 at the circumference of the cylindrical fitting F^ by a screw S, which 

 shutter can be set in any required position by moving the knob T, 

 or by rotating the entire condenser in or by its fittings. 



For the pui-pose of producing various effects of illumination 

 diaphragms are also used furnished with openings of various shapes 

 and sizes, placed either between the lenses B and C, or in front of 

 the smaller polished transmitting end of the catadioptric cone A. 



Cells for Minnte Organisms.*— In breeding Oribatid^, Mr. A. D. 

 Michael used glass cells each composed of an ordinary microscopical 

 glass slip 3 X 1 in., having in the centre, fastened by marine glue 

 or Canada balsam, a glass ring made of a transverse slice of glass 

 tubing about 3/4 or 7/8 in. in diameter, the length of the tube, and 

 consequently the depth of the cells, being usually about 3/8 in. The 

 tubing should be of tolerably thin glass, if very thick it is opaque, 

 and leaves little room inside the cell. Over this a thin glass cover, 

 rather larger than the diameter of the tubing, was laid, either a circle 

 or a square ; the latter is often handy, as the projecting corners are 

 convenient to take it on or off by, or sometimes a second slide or a 

 broken piece of one is more serviceable. This cover was always quite 

 loose, and simply held on by an ordinary brass-wire microscopical 

 spring-clip ; of course the upper edge of the slice of glass tube 

 required to be smooth, so that the cover would lie flat upon it, and 

 not allow the minute animals to escape. 



A cell so prepared was carefully cleaned out, and examined under 

 the Microscope, to see that it did not contain Acarina or ova. A small 

 piece of thick white blotting-paper, not largo enough to cover the 

 whole bottom of the cell, was then placed in it and damped ; a piece 



JJritibli Oribalidic, i. pp. 68-70. 



