Microscopy. 187 
with an opening 13 mm. indiameter. Resting upon this diaphragm, 
and corresponding with it in size and shape, is a second diaphragm 
of thin wax-cloth (Wd), which serves as a packing-washer for the 
ey-piece. 
The key-piece of the embryoscope consists of a low, metallic 
cylinder, closed by a disk of glass (G), which represents the window 
that is to cover the artificial opening in the shell. The upper part 
of the cylinder expands peripherally to form a rim with a milled 
edge. This rim has two notches opposite each other, into which 
fit the arms of a small wrench, by the aid of which the key-piece 
can be tightly screwed down. There is also a short, narrow, verti- 
cal canal (Vo) or vent, the lower end of which must open in the 
middle of the key-piece ring. 
The accessory apparatus required in the use of the embryoscope 
consists of (1) a trepan, (2) a guide-ring for the same, (3) a metallic 
Jork, and (4) the key or wrench before mentioned. 
_ The above-named pieces, together with a punch to cut wax-cloth 
ms, and six embryoscopes, may be obtained from Reiniger, 
a 
F edge of the diaphragm. 
e guide-ring for the trepan has the same construction as the 
