S8 FIRST LESSONS IN ZOOLOGY 



with the veins, and distributing the blood throughout the 

 tissues of the fin. 



" Observe that the blood consists of a fluid plasma, in 

 which floats numerous corpuscles. Observe that the 

 blood appears red in the arteries and veins, where the 

 corpuscles are accumulated, but only slightly reddish or 

 yellowish in the capillaries, where the 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: (i) 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, . . . not 

 very numerous, and usually seen trailing along the edges 

 of the blood currents, or escaping out into the tissues." 



The English sparrow (fig. 32). — As the English spar- 

 rows, which have spread over the whole country, are almost 

 universally held to be pests, the shooting of a few to serve 

 as specimens for the study of the external parts of a bird 

 may be looked on more leniently than the killing of other 

 birds should be. The habits of the live birds may be 

 studied as the pupils go and come from school. 



Examine a dead specimen. Note the division of the 

 body into head, trunk, and appendages — namely, wings 

 and legs. Note that the sparrow is covered with feathers, 

 some long, some short, in some places thick and in others 

 thin, but all fitting together to form a complete covering 

 for the body. Only the bill and feet are exposed, and 

 these are covered in one case (bill) with a horny sheath, 

 and in the other (feet) -with horny scales. The feathers 

 and the horny covering of bill and feet are simply modi- 



