1892.] 



THE MICROSCOPE. 



199 



74. Where can the eggs of the house JJy be obtained? — 

 Binocular. 



The house fly lays'its eggs In August, in stable marnu-e, and 

 they hatch in 34 hours. When found dip the eggs in boiling 

 water to kill them ; dry and mount them as opaque objects, or 

 drop them into carbolic acid and mount them in balsam, to study 

 the embryos. 



75. Does the Abbe condenser give as good a dark field illu- 

 mination as Wenha^n^s paraboloid^ or a polarizer? — C. A. B. 



The Abbe condenser is a high-grade illuminator, and used 

 with thin or minute objects. Wenham's paraboloid is best for 

 use with ordinary objects. The polariscope prism is not an 

 illuminator in the above sense. 



ITEAS 



Sectionizing Hydra Viridis. — About five years ago I tried 

 the experiment of growing the hydra from sections. I cut a large 

 and vigorous specimen into about ten pieces, and placed them in 

 a small test-tube with water drawn from the household tap ; in 

 two or three weeks, eight out of the ten pieces had developed in 

 full-grown vigorous hydr£e. Of course I was careful to exclude 

 all such things as cypris and Cyclops, and everything that seemed 

 likely to prey upon the undeveloped sections, and also allowed 

 plenty of water, so that there was no risk of the oxygen becoming 

 exhausted, a rather important feature where animal life is con- 

 cerned, either in development or prolongation. — B'. J. George., 

 in Science- Gossip for Azigiist. i8g2. 



The microscopic determination of rock-forming min- 

 erals. — A book, in Russian, bv F. Loewinson-Lessinof. bearing- 

 this title has been published in vSt. Petersburg. It contains tables 

 of the rock-forming minerals based on the writings of Rosenbusch, 

 Michel Levy, and Lacroix as well as of Doelter and Hussak. If 

 30U know the characters of the mineral, the book enables you to 

 determine its name. One table is based on examination with 

 polarized light. Others depend on external morphological char- 

 acters, the crystalline systems and other optical characters. About 

 So of the most practically important minerals are included and all 

 others are excluded. 



