LECTURE V. Q05 



and these vessels appear beautifully distri- 

 buted throughout the substance of the ani- 

 mal, frequently communicating like the 

 threads of network. In animals thus nou- 

 rished, in which there is no circulation, 

 there can be no distinct respiratory organs ; 

 neither do they want them, for their blood 

 or nutritive fluid is every where exposed 

 to circumambient air. 



In the animals included in the class of 

 vermes, according to the arrangement in 

 Professor Cuvier's lectures, many of which 

 have red blood, and therefore its motion 

 is more apparent, we meet with the first 

 generally acknowledged instance of cir- 

 culation. They have a dorsal vessel run- 

 ning the whole length of the animal, 

 which is large in the middle, and be- 

 comes gradually smaller towards either 

 end. Sometimes there are dilatations in 

 it, causing it to appear as if varicose ; and 

 there are lateral dilatations which may be 

 considered as hearts ; or the whole tube 

 may be regarded as the heart of the ani- 

 mal. This vessel is displayed in the Mu- 



