ii6 NATURAL SCIENCE. Aug.. 



longer and then removed to a shallow vessel containing distilled 

 water, for the double purpose of washing out the reagent and of 

 commencing to pick out the blastoderm from the yolk. 



The process of freeing the blastoderm from the yolk is a delicate 

 operation and more easily described than done, as it requires much 

 skill and practice in manipulation. The proportion of failures to 

 successes is at first very large. I proceed as follows. The egg 

 naturally falls upon its side, as represented in the accompanying 

 diagram. Fig. 2. The first manoeuvre is to spear it right through the 

 middle with a needle, in the spot to which the two arrows are pointing. 

 Then, the impaling needle being held still, a snip is made with 

 another needle in the direction of one of the arrows, after the manner 

 described above, and, immediately after, a second snip in the direction 

 of the other arrow, so as to cut the egg into two halves across its 

 equator. By this method, which is very easy after a little practice, 

 the egg with its enveloping chorion is cut in half cleanly and 

 sharply, Avithout injuring anything, in a way that would be impossible 

 with scissors or knife. One half, of course, contains the blastoderm 

 resting on a hemispherical mass of semi-fluid yolk, and enveloped in 

 a cup-shaped chorion. With a little care the yolk and blastoderm 

 can now be drawn right out of the chorion, which henceforth troubles 

 us no longer. 



We now have the blastoderm resting on a rather amorphous mass 

 of yolk. We may be either intending to stain the blastoderm in alum 

 carmine before it has been into alcohol, or we may wish to bring it 

 into alcohol unstained, and then colour it with hsematoxylin or 

 aniline stains. In the former case, the further removal of yolk is 

 best delayed till after staining. The yolk with the blastoderm still 

 adhering to it is carefully taken up on a lifter (of course, with the 

 blastoderm uppermost) and put into fresh distilled water in order to 

 wash out the Hermann's fluid completely, and thence it is taken 

 into alum carmine, where it should be left one to three hours. At the 

 end of that time it is put again into distilled water, when the yolk very 

 readily separates away clean from the blastoderm, the alum carmine 

 seeming to have a slightly macerating action on the yolk. If, on 

 the contrary, the. blastoderm is to be brought into alcohol without 

 staining, the process is exactly the same with the omission of the alum 

 carmine, the blastoderm being left longer in water in order to 

 macerate and separate off" the yolk. 



The blastoderm, stained or unstained, is now freed from yolk and 

 in distilled water. It is not all plain saiHng yet, however. When 

 the blastoderms come into the weaker grades of alcohol, they become 

 excessively sticky, and will adhere to the walls of the vessel, to the 

 needle, or to anything they touch, coming away from it in pieces 

 when detached. Moreover, they have a tendency to curl up. All 

 these unpleasant habits, however, can be cured by a simple device, 

 which I have also found applicable to other objects. It is as 



