ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 495 



of screws which work through arms mounted on a base, so as to raise 

 them above the surface of the stage. 



It will be seen that the metal substauce which is to be examined 

 can be set at any desired angle to the objective and also rotated, thus 

 obviating the necessity of mounting specimens on glass slips, and 

 rendering unnecessary the use of a levelling surface to the stage. 



The apparatus shown in the illustration is intended to be used with 

 a Microscope having a large central aperture, but another design is in 

 use for square stages, the outer edges of which are gripped by a frame 

 carrying the screws and jaws. 



Fig. 104. 



Certain Minute Structure observed in some forms of Tricera- 

 tium.* — A. A. Merlin notes that a variety of Triceratium parallelum 

 from the Oarnaru deposit, resembling the ordinary form in size, shape, 

 and general appearance, but not identical in detail, has been found to 

 possess a delicate lace work structure apparently covering the whole of 

 the silex composing the upper surface of the valve, and extending to aud 

 closely surrounding the primaries. Subsequently a similar but even 

 finer network was observed on the outer surface of a typical T. paral- 

 lelum. This is an excessively faint and difficult object and is close to 

 the limit of visibility with a fine Zeiss 3 mm. apochromat of N.A. 1*426. 

 illuminated by the full cone of Powell's dry adjustable apochromatic 

 condenser. The existence of an identical network has also been noticed 

 on a T. glandiferum (Grun), which could only be resolved and held for 

 brief intervals, after long rests to the eyes in the dark, by the employ- 

 ment of the above objective and a solid axial cone of about N.A. 1 ■ 3 

 from Watson's oil-immersion condenser. All the specimens were 

 mounted in styrax, and the author believes the appearances really 

 existent and not ghostly diffraction effects. 



Opto-Technics.j — In a paper read before the Socioty of Arts, Prof. 

 Silvanus Thompson eloquently pleads for the better organisation of 

 optical instruction in all its branches in London. He deprecates the 

 establishment of poZy-technics, believing that mowo-technics would be of 

 greater industrial service. Institutions devoted to the cu lture of special 

 subjects should be developed. Dr. Thompson considers that the Bolt 

 Court Institute, which is exclusively devoted to the technology of the 

 printing trades, is the most successful centre of technical education in 



* Journ. Quek. Micr. Club, viii. (1902) p. 267. 

 t Journ. Soc. Arts, 1. (1902) pp. 518-30. 



