33 



limbs of these tardigrade animals, as they 

 are called, and Doctor Macartney has 

 shewn that a similar arrangement of 

 vessels exists in the legs of fowls. Such 

 a distribution of the arteries may be sub- 

 servient without being essential to these 



modes of action. 



. 



In the human body we see instances 

 of irritability exerting itself after the man- 

 ner it does in general in tardigrade ani- 

 mals. If the iris had possessed the or- 

 dinary powers of muscles, and none else, 

 it could not have remained, as it is known 

 to do, permanently contracted in a strong 

 light, and permanently dilated in a weak 

 one. Indeed, an anatomist who is fond 

 of tracing structure as connected with 

 function, might readily persuade himself 

 that there is in the iris a distribution 

 of arteries, similar to that which Mr. 

 Carlisle has demonstrated in the limbs of 



B 



