132 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Microscope. The tail of tlie fish covers an aperture in the plate 

 closed with a piece of glass, and it is held securely in its place by a 

 ligature ; the caudal fin, which rests on the glass, is further secured 

 by a couple of springs. The box itself, which incloses the head and 



Fig. 26. 



gills of the fish, contains water which is constantly renewed by means 

 of two tubes, the upper of which, guarded by a screw-clamp, com- 

 municates with a vessel at a higher level, the lower conveying the 

 water away as fast as it is supplied. The stage must be inclined at 

 an angle of about 40". " The excellency of this method " (according 

 to Prof. J. Burdon-Sanderson *) " lies in the fact that the animal can 

 be kept under observation, without the use of any narcotizing drug, 

 for a long time in a perfectly natural condition." 



Dayton's Modification of the Wenham Half-disk Illuminator.! 

 Dr. E. Dayton, being convinced that the improved resolution of the 

 markings upon diatoms, when the V-shaped diajihragm was used, 

 consisted not so much in its cutting off the less oblique pencils of 

 light reflected from the mirror, but in the total exclusion of the dif- 

 fused rays emanating from the som'ce of illumination, describes a 

 modification by which the benefits arising from the use of the Wenham 

 half-disk are combined with those of the Woodward prism and V 

 diaphragm in a single apparatus. 



A brass slide, 3 in. by 1 in., A A (fig. 27, under-view ; fig. 28, 

 vertical section), has a circular bevelled opening, in which a corre- 

 spondingly bevelled brass disk B fits from above. Two latchets F F 

 are attached to the under surface of the disk, and allow it to rotate 

 freely in its bed without slipping out of the slide. In the disk B is 

 an opening exactly fitting the illuminator D. Dr. Dayton proposes 

 to cut away a portion of the lenticular edge of the latter, leaving a 



* ' Handbook for the Physiological Laboratory,' 1873, p. 229 (1 fig.)- In tlie 

 fig. the shape of the box diflers sliglitly from that in our text. 



t Proc. Amer. Soc. Micr., 5th Ann. Meeting, 1882, pp. IGl-3 (3 figs.). 



