14 ART. 3. — S. TKEDA : CONTRIBUTIONS 



is given in the place already cited, and therefore it suffices here to 

 say that it is a system of mirrors placed in the center of a small 

 dish which can he rotated around its vertical axis at will, and 

 has a graduated scale around its rim to enahle one to locate any 

 point exactly on its circumference. The upper view of an egg is 

 obtained by looking at it from above, as in any ordinary case of 

 examination by microscope. The view of its lower hemisphere is 

 reflected on a mirror, and is observed by slightly sliding the 

 dish and thus bringing the objective of the microscope above this 

 mirror. In a similar way, another mirror gives the reflection of 

 the lateral view of the egg, and by rotating the dish, and with 

 it the egg, a view from any point of its circumference can be 

 obtained. 1J 



Method : — My first care was of course to find a suitable 

 method for fixing an egg on the mirror-surface. I proceeded at 

 first in the manner of Pflüger. That is, an egg was taken out 

 of the frothy substance, with the thin layer of the innermost 

 egg-envelope, placed on the dry surface of the mirror and exposed 

 to the air for two or three minutes. When the egg seemed 

 safely fixed, water was poured into the revolving-dish by means 

 of a pipette, until the egg was submerged. This method was 

 not entirely satisfactory, for an egg fixed in this way was apt 

 to detach itself from the mirror surface, thus vitiating the 

 experiment. 



I next tried collodion which, I believe, has already been 

 used by some investigators. This was far from satisfactory, for 

 although it is a good fixative, it becomes opaque on the application 

 of water, and often kills the egg, probably by the injurions effect 



1) While this instrument has been designed for special use in investigations such as I 

 have undertaken, it has not, so far as I know, been used in the study of frog's eggs. 



