164 VERTEBRATES. 



which float numerous corpuscles. Observe that the blood 

 appears red in the arteries and veins, where the corpus- 

 cles are accumulated, but only slightly reddish or yellow- 

 ish in the capillaries, where corpuscles form but a thin 

 layer. 



Does the blood travel faster in the arteries and veins, or 

 in the capillaries ? 



Place a bit of cover glass over a very thin portion of the 

 fin, and study it with higher power. Find two kinds of 

 corpuscles in the blood : (1) red corpuscles (red only when 

 a number are seen together), very numerous, and carried 

 along in the center of the larger currents closely packed 

 together ; and (2) white corpuscles, resembling the amoeboid 

 corpuscles of the mussel and earthworm, not very numer- 

 ous, and usually seen trailing along the edges of the blood 

 currents, or escaping out into the tissues. 



External Features. Kill the fish with chloroform, and 

 make a closer study of its external features. 



Observe the exact correspondence of the two sides, 

 perfect bilateral symmetry. 



Observe the broad head, dorsally depressed, the absence 

 of neck, and the long, tapering body. 



On the upper surface of the head, just behind the mouth, 

 find four nostril openings, the posterior pair close behind 

 the barbels of this surface. Probe these openings with a 

 bristle to see whether they have any connection with each 

 other or with the mouth. 



Examine the bases of the large barbels at the corners 

 of the mouth, to find the bones which extend out into 

 them from the head. 



Examine the eyes. Are there any eyelids or other 

 means by which they may be closed ? Press on the edges 

 of the eyeball to discover how far it may be turned to look 

 in different directions. Press with a finger against the 



