THE FROG 31 



the kidney showing a Malpighian corpuscle and some adja- 

 cent 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 (&) the connection of 

 a tubule with the capsule. 



Look for nephrostomes ( funnel-like openings lined with 

 cilia) on the ventral surface of the kidney. These do not 

 appear in all the sections; if you succeed in finding one, draw 

 it under high power. 



VII. THE CIRCULATORY 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 low 

 power observe that the blood consists of a fluid portion, 

 the plasma, and solid elements, the corpuscles. Under 

 high power observe that the corpuscles are of two kinds, as 

 follows : 



1. Red corpuscles (erythrocytes), elliptical discs tinged 

 slightly red with haemoglobin. 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 drawing 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 the diaphragm of the microscope very small. 

 The white corpuscles vary considerably in size, form and 

 structure. The outline is sometimes irregular and under- 

 goes amoeboid changes. The usually large granular nucleus 



