20 THE FROG 
close to the lateral edge, and may be distinguished from neigh- 
boring 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 sur- 
rounded by an open space limited by a thin membrane (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; observe the 
cubical or columnar epithelium lining them. 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 the 
kidney showing a Malpighian corpuscle and some adjacent 
tubules; if possible, select for this purpose a section through a 
Malpighian corpuscle showing one or both of the following 
features: (a) the stalk by which the glomerulus is suspended 
within the capsule, and (b) the connection of a tubule with the 
capsule. 
Look for nephrostomes (funnel-like openings lined with cilia) 
on the ventral surface of the kidney. Draw a nephrostome under 
high power. 
VIII. Tue Circucatory System. 
A. The Blood.—Place a drop of blood on a slide; smear the 
-edge of a cover slip with vaseline and place it over the drop; the 
vaseline will prevent evaporation. Under the low power observe 
that the blood consists of a fluid portion, the plasma, and solid 
elements, the corpuscles. Under the high power observe that the 
corpuscles are of two kinds, as follows: 
1. Red corpuscles, elliptical discs tinged slightly red with 
hemoglobin. Are they thicker at the margin or in the center? 
Note the central nucleus. Draw a corpuscle as seen from the 
broad side; if possible find and draw an edge view. Each draw- 
ing should be at least two centimeters in its longer diameter. 
2. White corpuscles (leucocytes), generally about one-third 
the size of the red; they are best seen by making the opening of 
