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SUMMARY OF CURRENT RESEARCHES RELATING TO 



There is also a short, narrow vertical canal Vo or vont, the lower ond of 

 which must open in the middle of the key-piece ring. 



The accessory apparatus required in the use of the emhryoscope 

 consist of (1) a trepan; (2) a guide-ring for the same; (3) a motallic 

 fork ; and (4 J the key or wrench hefore mentioned. 



Vo 



Wd. 



Fro. 86. 



The trepan is a thin metallic cylinder, 2 to 2^ cm. long, the lower 

 end of which is toothed, while the upper part is fluted and serves as the 

 handle. The diameter of the trepan is a trifle smaller than that of the 

 opening of the diaphragm. The object of thiB is to leave a very narrow 

 zone of shell, covered with shellac, inside the inner edge of the 

 diaphragm. 



The guide-ring for the trepan has the same construction as the key- 

 piece, except that it has no glass disc. It serves to steady as well as 

 guide the trepan during the process of cutting. 



The fork has two notches at the ends of its prongs fitted to receive 

 the two bars of the mounting-ring. When adjusted to the bars, the 

 fork serves as a means of holding the emhryoscope securely while 

 screwing or unscrewing the key-piece. 



The wrench, the use of which has already been explained, is similar 

 in construction to the wrench used for mathematical instruments. 



The mounting-ring is fastened to the egg by means of a cement con- 

 sisting of two parts of wax and three parts of colophonium. The cement 

 is hard and brittle at the ordinary room-temperature, but becomes soft 

 and kneadable when held in the hand for a few moments. After 

 warming the mounting-ring over a gas or a spirit-lamp, a roll of the 

 softened cement is pressed into the space which must be completely 

 filled between the lower face of the diaphragm and the lower edge of 

 the ring. As soon as the ring becomes sufficiently cool, it is pressed 

 firmly to the equatorial surface of the egg, and the excess of the still 

 soft cement, wdrich is thus forced outward and inward beneath the ring, 



