932 SUMMARY OF CURRENT RESEARCHES RELATING TO 



air. Together with the NitzscJiia he found a Navicula, which moved 

 within the sheath, and which apparently could only have entered in 

 the form of a spore, and have developed there. 



In Schizonema he also observed the alternate forward and back- 

 ward movement of Naviculce within the sheath, single frustules 

 escaping through a small opening at the apex, which widened to allow 

 of their passage, and afterwards contracted, showing that the mem- 

 brane of the sheath must be elastic and flexible. The author came 

 to the conclusion that the sheath-apparatus served solely for the pur- 

 pose of the multiplication of the Naviculcp,, and tbat the name ScJiizo- 

 nema ought to be applied, not to the sheath, but to each separate 

 enclosed frustule. He concludes that the genera Homeocladia, Berlce- 

 leya, Encyonema, and BicMea must be identified with Nitzschia, 

 Amphipleura, Gymhella, and Navicula. 



MICROSCOPY. 



o. Instruments, Accessories, &c. 



Descriptions of New Microscopes. — Some of our correspondents 

 appear to be afli'onted because in the accounts which we give of new 

 Microscopes we omit by far the larger part of the descriptions usually 

 sent us. 



We do this advisedly, as we invariably give a figure, which at once 

 dispenses with any necessity for a full description of those parts which 

 are seen at a glance on referring to the drawing. Whilst in a cata- 

 logue or a treatise intended to describe various leading types of Micro- 

 scopes, full descriptions may properly be included, it can be of no 

 value to the readers of this Journal to have such paragraphs as this 

 attached to a woodcut : — 



" The Microscope consists of a base A in the form of a horse-shoe, 

 in which is inserted an upright pillar B. To this pillar is attached a 

 bar C, which by means of the hinge D can be placed in any position 

 from the vertical to the horizontal. This bar carries at its lower end 

 a ring E, which holds on the one side a plane and on the other a 

 concave mirror. F is the stage," &c. &c. 



For the purposes of this Journal, all that can be required in addi- 

 tion to a woodcut is a reference to such points as are special to the 

 particular form. 



Lacaze-Duthiers' Aquarium Microscope (Ross Tank Microscope). 

 — This (Fig. 203) was devised by Professor Lacaze-Duthiers for use in 

 aquaria, or for examining vertical surfaces, and has been somewhat 

 modified by M. Nachet since the first model of 1864. 



A column upon a tripod supports an aim at the extremity of which 

 is the Microscope-body, which can be adjusted to the object in two 

 rectangular directions by the two screws seen on the edge of the 

 " drum " through which the tube passes. The " drum " contains the 

 sliding metal rings by means of which the rectangular motions are 

 obtained. The focussing is by rack and pinion (milled head shown 

 at the side of the tube). The Microscojie can also be revolved on 



