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Entomology and Zoology 



fhe distortion mav be eliminated in either ol two w.i\s. I ho 

 tirst and best is to sel the orientation guide .it an agle ol about 45 

 degrees from the axis ol the object and cul the sections at right 

 angles to the orientation guide and hence obliquely to the specimen. 

 I he reconstruction lines are drawn in tlu- same wav except that the 

 projection oi the orientation line is allowed to fall in the same place 

 each time, thus eliminating the displacement and consequent distor- 

 tion, it is hard, however, to get .1 clear idea ol the relations ol 

 parts from oblique sections. IThe reconstruction does not show 

 am more than one that follows the first method, and each series is 

 good for reconstructing onl) one aspect, 



Phe other \\.i\ ol getting rid ol the distortion is to insert .it the 

 place ol proper magnification in the cone ol light rays from the 

 projector .1 lense ol sufficient curvature to refract the rays into .1 

 parallel bundle. B) tilting the drawing board .it .1 proper angle to 

 this bundle the field will be caused to t.ill in such an ellipse as to 

 eliminate .uw distortion. I Ins angle is one whose tangent equals 

 the displacement divided h\ the product ol the thickness ol the sec- 

 tion tunes the magnification in diameters. 



Occasionally wrinkling ol the section in cutting or in mounting 

 occurs ami renders it neeessar) to disregard the orientation guide 

 It is easy, however to put the section in approximately its right 

 place ami to check :t up In the next section. In reconstructing svm- 

 metrical specimens where there is a clearl) marked axial line it is 

 often possible to dispense with the orientation guide and to place 

 die successive sections from landmarks whieh the\ themselves bear. 



\\ \ roNn 



The brain (Fig. 1. -. 4) is a verj complex structure. Popo- 

 graphicall) it is divided into two parts, the dorsal ami ventral In 

 the central mass ol muscle ami blood \ essels (Figs. 5, 6, 7: q), 

 which tissue, going forward from between the central part ol the 

 brain and the visceral ganglion, pinches out into a muscular sheet 

 at either side ami separates the six dorsal lobes from the eight to 

 ten ventral lobes or branches ol the lore part ol the brain. The 

 brain is symmetrical ami is divided into lateral halves bv a septum 

 whieh continues as a canal through the main brain (Fig, 6 : w) 



