Chapter XVI: Some Embryological Methods 115 



Decolorize until the embryo becomes bright scarlet in color, then 

 wash in 70 per cent, alcohol and leave it there until ready to 

 proceed. 



10. Transfer the object through 95 per cent. (1 hour) abso- 

 lute alcohol (2 hours) to xylol, where it should remain about 2 

 hours or until it ceases to appear opaque. 



Moant two embryos entire, one with the ventral, the other with 

 the dorsal side uppermost. Put bits of broken cover-glass under 

 the edges of the cover to avoid crushing them. 



The three remaining embryos are to be so sectioned (step llff.), 

 that the student will have a complete series of sections in 

 each of the three different planes of the body with reference to 

 the axis of the spinal cord: viz., transverse, sagittal, and frontal. 

 Read carefully memorandum 12 on orientating serial sections. 



CAUTION. Before sectioning any embryo always make an 

 outline drawing of the entire embryo, then rule lines across the 

 drawing parallel to the plane of section. Unless this is done 

 great difficulty will be experienced frequently in understanding 

 the sections. 



11. Infiltrate the embryo with paraffin in the usual manner by 

 leaving it in melted paraffin for 2 or 3 hours. A softer paraffin 

 (melting at 43 C.) than has been used heretofore may be 

 employed and the sections cut thicker (15 to 20 microns). 



12. Imbed and cut in the usual way (chap. v). Mount the 

 entire series. 



MEMORANDA 



1. For the Average Course in Embryology of the Chick the following 1 

 mounted stages are the most useful : 

 I. Mounted in toto. 

 Approximately, 



48 hours viewed from above and below. 



>C a a a a a a 



30 " " 



; I a ' a a a a 



i o a u u a 



10 u a u u 



64_72 ' 



96 hours (studied in alcohol under the dissecting microscope). 



