ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 263 



In some remarks on the use of the apparatus it is pointed out * 

 that it shows the value of wide apertures for good definition, for if a 

 preparation of the proboscis of the blow-fly be observed with an inch 

 objective having an air angle of 30°, the view is superb, the pseudo- 

 tracheal markings come out well-defined and sharp ; but close the 

 shutter until an angle of 14^ or less is obtained, and examine again, 



Fig. 49. 



Fig. 48. 



when it will be found that the definition is not nearly so good, while 

 there is more penetration, the whole of the pseudo-tracheal tube being 

 observed under one focussing. While in this condition, the eye being 

 still applied to the tube, open the shutter to its full extent, and the 

 effect of wide aperture will demonstrate itself. 



" Perhaps the best object to show the amount of penetration 

 possessed by objectives of low angle, may be found in the micro- 

 fungus, Myxotrichum deflexum, or M. chartarum, observed under the 

 1-inch objective. The former object consists of little patches of grey 

 downy balls, from which arise a number of radiating threads, fur- 

 nished with a few opposite and deflexed branches. Under an inch 

 objective of 30° air angle, but few of these branches can be seen 

 under one focussing, the remainder being enveloped in a haze of 

 light ; but if a central layer be focussed, the simple closing of the 

 shutter will suffice to bring the superior and inferior layers into view, 

 though, of course, the image is not so bright and well defined as 

 before." 



Gundlach J-inch Objective f — Dr. L. Curtis recently exhibited to 

 the State Microscopical Society of Illinois a new ^-inch objective 

 made by Gundlach, and claimed by the maker to have an angle of 

 100°. The back lens is large, and extends beyond the border of the 

 opening in the screw. This opening, therefore, acts as a diaphragm. 

 In order to secure the benefit of the full aperture, the portion of the 

 objective can be removed, and an adapter furnished with the Butterfield 

 broad gauge screw can be substituted. It has also another screw of 

 about the same diameter as the Butterfield screw, but provided with 

 a finer thread. The name and description of this screw were not 

 known. The front of the objective is ground down to a conical 



* North. Micioscopist, ii. (1882) pp. 13-14 (2 figs), 

 t Science, iii. (1882) pp. 19-20. 



