320 SUMMARY OF CURRENT RESEARCHES RELATING TO 



escape of the liquid and of the object enclosed within the tube, the object 

 may be pricked or perforated at any selected point by a sharp tap. If 

 mauijjulated with more caution, the stylet also serves to turn the object 

 round within the tube, and the combination of this movement with that of 

 turning the tube permits examination in any position whatever. A lever 

 serves to control the sliding of the stylet by reducing by five to ten times 

 the extent of the movement imjiarted by the hand. This lever is a blade 

 of straw, through the fixed end of which passes a pin fastened vertically to 

 one of the corners of the flat slide. Its direction is perpendicular to the 

 stylet, with which it is connected at about 1"5 cm. from its fixed end. 

 This lever moves in the plane of the flat slide, beyond v^hich it projects, 

 as it is much longer than the slide is broad. 



By the aid of this perforator the author has been able to pierce and 

 kill, at will, any cell of an ascidian egg in segmentation, and to obtain 

 experimentally the " monstres " called " fractions d'individu," the existence 

 of which he discovered. 



Bausch & Lomb Condenser and Substage. {^Post.'] 



The Microscope, VII. (1887) p. 16 (1 fig). 

 Heurck, H. van.— Comparateur a employer dans les recherches microscopiciues. 

 (Comparator for microscopical researches.) \_Post.'\ 



Bull. Soc. Belg. Mkr., XIII. (1887) pp. 76-8 (2 figs.), 

 RoHRBECK. — Ueber Thermostaten, Thermoregulatoren, und das Constantbalten von 

 Temperaturen. (On Thermostats, Thermoregulators, and the maintenance of Con- 

 stant Temperatures.) Deutsche Medicinal ztg., 1886, and Deutsche Chemikerztg., 1886. 

 Of. Centmlbl. f. Bacterial, u. Farasitenk., I. (1887) pp. 247-8. 



(5) Photomicrography. 



Evans's Focusing Screen for Photomicrography.* — Mr. P. H. Evans 

 refers to the difficulty which exists in focusing, by means of an ordinary 

 focusing lens, the microscopic image projected on a screen of patent plate 

 glass. This is due to the power of accommodation of the eye, in conse- 

 quence of which the focal plane of the image is frequently assumed to be 

 on the outer instead of the inner surface of the screen. He suggests that 

 this difiiculty may be readily overcome by ruling on the inner surface of the 

 glass screen (i. e. the surface towards the Microscope) a series of fine lines 

 similar to those shown in fig. 83 ; the eye has then before it a definite 



Fig. 83. 



object in the focal plane upon which the focusing lens is adjusted, so that 

 the almost involuntary movement of accommodation is practically arrested 

 thereon, and the focusing of the microscopic image on that plane is thus 

 greatly facilitated, 



* Journ. and Trans. Phot. Soc, xi. (1886) pp. 25-8 (1 fig.). 



