CEPHALOPODA. 639 



form, in powers, in modes of life, from those which more obviously 

 attract the interest of the anatomical Teacher, that some apology may 

 seem necessary for the devotion of an entire course of Lectures, in 

 the theatre of a College of Surgeons, to the lowest and most minute 

 forms of animal life. 



We learn, indeed, with little surprise, that the import of the dissec- 

 tions of the Invertebrate animals, by the busy care-worn practitioner 

 who, in the last century, prepared the most instructive illustrations 

 of these lectures, were not understood ; and that these occupations of 

 Hunter were regarded by some of his contemporaries as a kind of 

 laborious trifling. But the question of " cui bono ? " which might 

 then be pardonable, would be inexcusable at the present day, when 

 the relations of Surgery as a science to Physiology, and the depend- 

 ence of Physiology upon Comparative Anatomy are so much better 

 understood : and I trust that a brief retrospect of some of the deduc- 

 tions from the details of Invertebrate Anatomy will suffice to de- 

 monstrate their indispensable value to all who are interested in the 

 progress of physiological science. 



The Invertebrated classes include the most numerous and diversi- 

 fied forms of the Animal Kingdom. At the very beginning of our 

 inquiries into their vital powers and acts we are impressed with their 

 important relations to the maintenance of life and organisation on 

 this planet, and their influence in purifying the sea and augmenting 

 and enriching the land — relations of which the physiologist con- 

 versant only with the Vertebrated animals must have remained 

 ignorant. At our first entrance, and by the lowest portal, into the 

 vast and intricate repositories of the animal mechanisms, we are at 

 once introduced to the phenomena of spontaneous fission and ciliary 

 motion, of the generality and importance of which in the animal 

 economy each day seems to bring fresh proof, but which are most 

 conspicuously manifested in the monads. 



The physiologist must have remained in ignorance of the most 

 instructive modifications and combinations of the principal organs of 

 the animal frame, if the researches of the Comparative Anatomist 

 had been confined to the Vertebrated animals, or those which are 

 constructed on the same general type as ourselves. Without a much 

 deeper investigation, we never could have understood the relative 

 importance of the different organs, the order of their introduction 

 and progressive complication, their homological and analogical 

 relations. 



Only in the Invertebrated classes do we find examples in which 

 the lungs, like the liver, are supplied by the ramifications of the 

 trunk of a vein without the interposition of a heart. Only in the 



