COMPRESSORIUM ZOOPHYTE TROUGHS. 



these instruments, and all such intended for real use should 

 be reversible, so that the objects maybe easily viewed from 

 both sides, and this can be done with the form shown in 

 Fig. 72. 



FIG. 72. 



A form of compressor differing from all others has been 

 devised by Mr. Holman, U.S.A. ; the top or mica cover 

 is fixed while the lower thicker plate of glass is raised 

 or depressed by means of a screw-nut and spiral spring. 

 The employment of a thin mica cover is certainly an im- 

 provement, and one which English opticians would do 

 well to follow. In this we 

 imagine every practical 

 microscopist will concur, 

 as the breakage of a glass 

 cover in the middle of an 

 interesting observation is, 

 to say the least, vexing. 



Zoophyte troughs may 

 be easily constructed by 

 the student ; the form 

 shown in Fig. 73 is made 



FIG. 73. 



of a thick glass base plate and ends, while two pieces of 

 thinner material furnish the front and back, which should be 

 of the same thickness as the thinnest slips are cut from. 

 This trough should measure T ^ of an inch in width, 



