16 The Microscope. 



For later periods of incubation than those mentioned, the reader 

 must consult such works as Foster and Balfour's " Elements of 

 Embryology," Balfour's " Comparative Embryology," or the less 

 voluminous work of Prof. Packard, " Outlines of Comparative 

 Embryology," all of which should be found in every public library 

 of any considerable size. 



It is supposed, of course, that before taking up the subject of 

 which these papers treat, the student has familiarized himself with 

 the use of the microscope and microscopical technique, as already 

 taught in the Elementary Department of this journal. 



SECTION I. 



APPARATUS : REAGENTS. 



§ 1. Embryology, from the Greek words E/zCpuor, an embryo, 

 and ^"^oyo-, a treatise, treats of "those successive modifications 

 through which the organism passes in its development from the 

 germ to the adult form." 



It is a most important branch of biology, and concerns the 

 development both anatomical and physiological of every living 

 object. 



In the present series the embryology of the domestic fowl has 

 been chosen to initiate the beginner into the subject, for two reasons; 

 first, because eggs can be procured at all times and ifi all places; 

 and second, on account of the ease with which the microscopical 

 appearances can be made out. 



§ 2. The necessary apparatus is such as may be found in the 

 armamentarium of the general microscopist, and will be mentioned 

 in the descriptions of the methods given. 



Certain reagents, etc., however, must be at hand. These are: — 



(a). A one per cent, solution of common salt. 



(6). A three per cent, solution of chromic acid. 



(c). A solution of osmic acid. 



1 cc. of a one per cent, osmic acid solution. 

 100 cc. water. 



Mix. 

 Label. — Osmic Acid Solution. 



N. B. Keep in a dark glass bottle, or cover the bottle with 

 black paper or plush, as the solution soon deteriorates in the light. 



