THE EMBRYOLOGY OF THE HONEY BEE 253 



ually. If this is not done, distortion will almost inevitably result. 

 In cases where the chorion is not opened, or opened insufficiently, 

 a transfer from alcohol to clearing fluid will cause the egg to be 

 completely flattened by osmotic pressure, owing to the slight re- 

 sistance of the yolk. Clearing may be quickly and easily accom- 

 plished by the following method of flotation, suggested by Dr. 

 Petrunkewitsch : A small quantity of pure cedar oil is poured 

 into the bottom of a narrow vial. On the top of this are poured 

 successive layers containing an increasing proportion of absolute 

 alcohol. In practice these were : pure oil, two-thirds oil, one-third 

 oil. On the top layer the embryos were placed surrounded by 

 pure absolute alcohol. They then descend gradually to the bottom 

 of the vial, when they may be taken out, washed in pure cedar 

 oil and transferred to balsam, if they are to be mounted for study 

 entire. If intended for sections they were placed in xylol before 

 transfer to paraffin. Embedding was done in watch crystals. 

 Paraffin of fifty-five degrees C. melting point was used, the eggs 

 remaining in the paraffin from one-half to an hour to three hours". 



It is extremely desirable to orient the embryo accurately. This 

 was accomplished by placing the watch crystal containing the 

 melted paraffin and the embryo on a piece of clear glass, slightly 

 warmed, and placing the whole on the stage of a binocular micro- 

 scope. A layer of partially cooled paraffin, sufficient to support 

 the embryo in any position soon forms at the bottom of the watch 

 crystal, and the embryo may be placed in this in the position 

 desired. In practice the ventral face was placed uppermost. The 

 watch crystal was then floated on a vessel full of cold water, and 

 the paraffin subsequently hardened by complete immersion. 



Sections were cut by means of a Minot microtome, five to seven 

 microns in thickness, according as the conditions were favorable 

 or otherwise. 



Summary 



The elongate cylindriform egg is slightly curved in the long 

 axis and, with reference to the future embryo, presents a slightly 

 larger cephalic end, and a convex ventral, as opposed to a con- 

 cave dorsal surface. Two membranes cover the egg, an outer, 

 the chorion, and an inner, the vitelline membrane. The chorion is 

 extremely thin, transparent, and covered with minute papillae 



