3O THE FROG 



the fat bodies may be included in the drawing. This draw- 

 ing should be about twice natural size. 



How do the eggs produced in the ovary of the female 

 reach the exterior? 



B. Reproductive Cells. If you have not already done 

 so, make a microscopical study of the immature ovarian 

 eggs and the ripe spermatozoa of the frog. Directions will 

 be found on page 14. 



C. The Finer Structure of the Kidneys. In transverse 

 sections of a kidney distinguish median and lateral edges, 

 dorsal and ventral surfaces. The dorsal surface is usually 

 more convex, the lateral edge more acute. 



In a cross-section, find the ureter; this lies on the dorsal 

 side close to the lateral edge, and may be distinguished from 

 neighboring blood vessels by the columnar character of the 

 epithelium lining its walls, and by the absence of blood 

 corpuscles. 



The Malpighian corpuscles lie nearer to the ventral than 

 to the dorsal surface; each consists of a rounded or oval 

 body, the glomerulus, formed by a cluster of capillaries and 

 nearly surrounded by an open space limited by a thin mem- 

 brane (Bowman's capsule). At one point the glomerulus 

 is suspended by a short slender stalk which naturally does 

 not appear in all the sections. 



The uriniferous tubules are cut in various planes; ob- 

 serve that their walls are composed of ciliated columnar epi- 

 thelium. Each tubule starts in a capsule (usually opposite the 

 stalk of the glomerulus) and after a complicated course 

 opens into the ureter. Try to find the beginning of a tubule, 

 where it connects with the capsule. 



Under high power, draw a portion of a cross-section of 



