CEPHALOPODA. 371 



The Mollusca pass from the condition of the ciliated Monad to that 

 of the shell-less Acephalan, and in like manner either remain to work 

 out the perfections of that stage, or diverge to achieve the develop- 

 ment of shells, of a head, of a ventral foot, or of cephalic arms, with 

 all the complexities of organisation which have been demonstrated in 

 the concluding Lectures of this Course. 



The Vertebrated ovum having manifested its monadiform relations 

 by the spontaneous fission, growth, and multiplication of the primordial 

 nucleated cells, next assumes, by their metamorphosis and primary ar- 

 rangement, the form and condition of the finless cartilaginous fish, 

 from which fundamental form development radiates in as many and 

 diversified directions and extents, and attains more extraordinary 

 heights of complication and perfection tlian any of the lower secondary 

 types appear to be susceptible of. The ultimate stages of these de- 

 velopments, the various permanent or mature structures of the Verte- 

 brated series, with their physiological and other relations, will form 

 the subjects of succeeding lectures. 



For the kind and patient attention with which the present course 

 has been honoured, I must again, Mr. President and Gentlemen, 

 express my most sincere thanks^ and, with every good wish, respect- 

 fully bid you Farewell ! 



To Mr. Cooper's notes of the Lectures, as orally delivered, I have 

 added the details contained in my written notes, which, for want of 

 time, were omitted, or only briefly alluded to in the theatre. R. O. 



B B 2 



