250 PRACTICAL DIRECTIONS. [APP, 



embryo flat upon it, having removed as much super- 

 fluous Bergamot oil as possible, and then pour in 

 some more of the spermaceti mixture, which should 

 be as hot as can be used without injuring the object. 

 With a hot needle, move the object about so as to 

 get rid of all air bubbles, and to assist the sperma- 

 ceti in penetrating all parts of the embryo. Finally, 

 before the spermaceti becomes solid, place the 

 embryo in the position required for subsequently 

 making sections ; and when the whole becomes 

 solid, make a mark over the position of the embryo. 

 It is better to soak the object in the hot spermaceti 

 before finally imbedding it, but the manipulation of 

 this is rather difficult with embryos of this age. 



If successfully imbedded, the spermaceti will be 

 found to have penetrated through and through the 

 embryo ; and the method has the great merit of per- 

 mitting the imbedding medium to be quite easily 

 dissolved away from the sections, by a few minutes' 

 immersion in a mixture of four parts of turpentine 

 to one of creosote. With the other imbedding 

 materials of which we have spoken, this cleaning 

 of the sections is very troublesome and difficult, and 

 liable to result in injury to the specimens. 



4. CUTTING SECTIONS. 



When the imbedding block is cold pare away 

 the edges and then gradually slice it away until the 

 edge of the area opaca appears. The sections must 

 then be made more carefully, and each one ex- 

 amined till the actual body of the embryo is arrived 

 at. 



It is best to begin with transverse vertical 

 sections which may commence either at the tail or 

 head end. The latter is preferable, since the bit 

 which is last cut is apt to slip. 



A section instrument may be used ; but we our- 

 selves very much prefer a simple razor provided 

 with heavy fixed handle (i.e. with no hinge) held 

 in the hand. 



