APP.] OPENING THE EGG. 487 



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 pi-eserved 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 difficult ; 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 vindesirable 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 ^g^, 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''C. 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, 



