BLOOD. 



35 



direction, and frequently send out side-bran dies, which 

 presently return into the stream from which they is- 

 sued, or unite with others in a very irregular network. 

 These are the capillaries, which feed the veins, and 

 which are themselves 

 fed by the arteries, 

 whose course is in the 

 opposite direction, viz., 

 from the body. These, 

 however, are with diffi- 

 culty seen : they are 

 more deeply seated in 

 the tissues, and are less 

 spread over the webs, 

 being generally placed 

 along the borders of the 

 toes ; they are, more- 

 over, fewer and smaller 

 than the veins ; but the 

 blood in them usually 

 flows with more impetuous rapidity. 



The variations in the impetus of the current which 

 we observe in the same vessel are probably owing to 

 the mental emotions of the animal ; alarm at its un- 

 usual position, and at the confinement which it feels 

 when it endeavours to move, may suspend the action of 

 the heart, 'and thus cause an interruption in the floAv ; 

 or analogous emotions may quicken the pulse. "We 

 will, however, now release our little prisoner, who, 

 though glad to be at liberty, is, as you see, none the 

 worse for his temporary imprisonment. 



Let us now look at the circulation of the blood in 

 one of the Invertebrate Animals. In this thin glass cell 



CIROITLATION IN FEOGS FOOT. 



