EMBRYOLOGICAL METHODS. 333 



camera drawings is described by WOOD WORTH (Zeit. f. wiss. 

 Mik., xiv, 1, 1897, p. 15) : 1. Draw an axial line of the 

 length of the object multiplied by the magnification em- 

 ployed. 2. Measure with a micrometer the greatest dia- 

 meter of each section. 3. Plot these diameters down 

 transversely on the axial line at distances corresponding to 

 the thickness of the sections multiplied by the magnification. 

 4. Join the extremities of these diameters ; this will give you 

 an outline of the object. 5. Measure off on each section the 

 nearest and farthest limits (from the margin) of the organs 

 to be filled in, and plot them down on the transverse lines 

 (3), and join the points as before, i. e. from section to 

 section ; this will give you the outlines of the organs. 



This process is best applicable to reconstruction from trans- 

 verse sections, but it can be applied to reconstruction from 

 sections in any plane if the object can be provided with a 

 plane of definition at right angles to the plane of section. 

 This may be established by cutting off one end of the 

 object, or the like (see also Orientation, 133, 155). 



Mammalia. 



589. Rabbit Dissection, For the study of the early stages 

 the ova must be sought for in the tubse a certain number of 

 hours after copulation. The dehiscence of the follicles takes 

 place about ten hours after the first coitus. The tubse and 

 cornua having been dissected out should be allowed to cool, 

 and remain until the muscular contractions have ceased. 

 Then, with the aid of fine scissors or a good scalpel, all th& 

 folds of the genital duct are carefully freed from their 

 peritoneal investment. 



The tubae are then (if the ova are still within them, which 

 is the case up to the end of the third day after coition) laid 

 out on a long slip of glass, and slit up longitudinally by means 

 of a pair of fine, sharp scissors. By means of needles and 

 forceps the tubal mucosa is spread out so as to smooth out 

 its folds as much as possible, and is carefully looked over 

 with a strong lens or with a lower power of the microscope. 

 When the ova are found, a drop of some " indifferent " liquid 

 is dropped on each, and it is carefully taken up with the 



