440 PRACTICAL DIRECTIONS. [AfF. 



The transference may easily be effected, if both 

 the watch-glass and slide are plunged into a basin of 

 clean warm salt solution. "With a little care, the 

 blastoderm can then be floated from the one to the 

 other, and the glass slide, having the blastoderm with 

 its upper surface uppermost spread flat upon it, very 

 gently raised out of the liquid. 



A thin ring of putty may now be placed round 

 the blastoderm, a small quantity of salt solution 

 gently poured within the ring, and the whole covered 

 with a glass slide, which may be pressed down until 

 it is sufiiciently close to the embryo. The presence 

 of any air-bubbles must of course be avoided. 



Provided care be otherwise taken to keep the 

 embryo well covered with liquid, the putty ring and 

 the coverslip may be dispensed with. They are often 

 inconvenient, as when the embryo has to be turned 

 upside down. 



The object is now ready for examination with a 

 simple lens or with a compound microscope of low 

 objective. It is by far the best for the student to 

 begin at least with the simple lens. In order that 

 everything may be seen at its best, the slide should 

 be kept warmed to about 38°, by being placed on a 

 hot stage. 



D. Surface view of the transparent embryo 

 from, above. 



The chief points to be observed are : 



1. The head-fold. 



2. The indications of the amnion; especially the 

 false amnion, or outer amniotic fold. 



