i8 9 3- 



SOME USEFUL METHODS IN MICROSCOPY. 



115 



that while its point scrapes along the bottom of the vessel its edge 

 scrapes against that of the stationary needle, an exceeding sharp and 

 clean cut can be made through the jelly, which is snipped as cleanly 

 as with a pair of scissors. (See accompanying Fig. 1 and explana- 

 tion.) With three or four such snips, which, with practice, occupy 

 as many seconds, the chorion is almost completely denuded of its 

 adherent jelly, without the blastoderm suffering the least injury. In 

 Sepia the outer coats of jelly may be removed by simply cutting 

 them with scissors and cautiously squeezing out the egg. 

 b 3 6*. i' 



Fig. 3. 



Fig. 1. — Diagram to illustrate the, method of snipping an object in two with 

 two needles, a the stationary needle, b 1 , b-, b 3 , three positions of the moving needle, 

 0, object, cd bottom of the vessel. The arrows and the dotted lines indicate the 

 direction in which b moves. The object is at first enclosed in a triangle, xyz, the 

 plane of which should coincide with the plane in which it is to be cut. As b moves 

 the triangle xyz is reduced to a point, and the object, if soft, is irresistibly cut in 

 two in the plane of xyz. 



Fig. 2.— Cephalopod Egg. — bl. Blastoderm, ch. Chorion, y. Yolk. /. Fragments 

 of Jelly. 



Fig. 3. — Diagram to explain section-cutting (p. 122). 



We now have the egg enveloped only in the chorion, with the 

 minute disc-shaped blastoderm at one end. The blastoderm is 

 transparent and almost invisible. The egg is now removed from the 

 sea-water and dipped into a capsule containing Hermann's fluid. 

 After a few seconds the blastoderm shows up very plainly as an 

 opaque white patch. It should be left for about a minute 



