CH. XI] SERIAL MICROSCOPIC SECTIONS 405 



the slide that under the compound microscope the aspects will be 

 as in the observer's body; then it will be easy to locate objects at the 

 right or left, dorsal or ventral. 



(3) Remember that in the ribbons the surfaces are somewhat 

 unlike in appearance. The lower surface, that is the surface facing 

 the section knife, is shiny, while the opposite surface is dull. This 

 knowledge is important, for sometimes sections get turned over acci- 

 dentally. It is unfortunate to have part of the sections of a series 

 wrong side up. 



(4) The aspect cut first will face upward on the slide, that is, if 

 the head is cut first the cephalic aspect will face up; if the left side 

 is cut first the sinistral aspect will face up, and if the dorsal side, the 

 dorsal face will be up. 



(5) The aspect of the embryo which first meets the edge of the 

 knife will be at the beginning of the series. If arranged and cut as 

 here directed, transections would have the right side of each section 

 toward the left on the slide (fig. 239). Under the compound micro- 

 scope it would appear on the right. 



For sagittal sections where the caudal end meets the knife, the caudal 

 end of the section would be toward the left on the slide (fig. 242). 



For frontal sections (fig. 240) where the right side meets the knife 

 edge first, the right side of each section will be toward the left end 

 of the slide. 



660. Mounting. Cut the ribbons into segments of equal length, 

 using preferably a curved knife (fig. 223). Transfer to albumenized 

 slides with fine forceps (fig. 225). Make parallel with the long axis 

 of the slide, and put the first section at the upper left-hand corner 

 (fig. 237). 



In a word, decide on some good plan for mounting series and follow 

 the plan consistently. 



661. Size of slides and cover-glasses for series. (i) If the 

 object is small, the standard slide 25 x 75 mm. (fig. 185) is good and 

 the cover-glass can be either 22 or 23 mm. wide and 50 or 60 mm. 

 long. The smaller sizes are to be preferred when convenient, for more 

 space is left to the label, and the cover-glass is not too near the edge 

 as with wide covers. 



