APP.l OPENING THE EGG. 437 



in the ordinary way (B, a) should be stained slightly, 

 dehydrated, soaked in oil of cloves until transparent 

 and mounted in balsam. 



Whole embryos of a later date cannot be satis- 

 factorily preserved as microscopic objects. 



Practical directions for obtaining and studying 

 CHICK Embryos. 



II. Examination of a 36 to 48 hours' embryo. 



The student will find it by far the best plan to begin 

 with the study of an embryo of this date. The manipu- 

 lation is not diflB.cult ; and the details of structure are 

 sufficiently simple to allow them to be readily grasped. 

 Earlier embryos are troublesome to manage until some 

 experience has been gained; and the details of later 

 ones are so many as to render it undesirable to begin 

 with them. 



A. Opening the Egg. 



Take the egg warm from the hen or the incu- 

 bator, and place it (it does not matter in what posi- 

 tion, since the blastoderm will at this stage always 

 be found at the uppermost part of the egg) in a 

 small basin large enough to allow the egg to be 

 covered with fluid. It is of advantage, but not 

 necessary, to place at the bottom of the basin a 

 mould, e.g. a flat piece of lead with a concavity on 

 the upper surface, in which the egg may rest securely 

 without rolling. Pour into the basin so much of a 

 ■75 per cent, solution of sodium chloride warmed to 

 38°0. as will cover the egg completely. With a sharp 

 tap break through the shell at the broad end over 

 the air-chamber, and let out as much air as has 

 already been gathered there. Unless this is done, 



