54 DVBLEH UNIVERSITY 



cavity of the body, and the reproductive organs arc external. In the 

 second division, known as Actinozoa, the wall of the alimentary 

 canal is usually separated by a wide interval from the common pa- 

 rietes, and the reproductive organs are lodged in the interior of the 

 cavity so formed. Now, each of the old classes, Zoophyta and Acalephae, 

 contain forms belonging to both of the above divisions, so that it is de- 

 sirable to abolish the terms in question as founded upon crude and 

 superficial considerations. The author illustrated this part of his subject 

 by demonstrating the anatomical distinctions between the Ciliogradc 

 and naked-eyed Medusse. The relations subsisting between these several 

 groups may, perhaps, be best indicated by reference to the accompanying 

 table :— 



RADIATA CCELENTERATA. 



[of moderns). 



1. ZoornYTA. 



1. Hydroida, Hydeozoa. 



2. Asteroida, Actinozoa. 



3. Helianthoida, Ditto. 



2. Acalephae. 



1. Discophora, Hydeozoa. 



2. Siphonophora, Ditto. 



3. Ctenophora, Actinozoa. 



3. ECHINODEEMATA. 



Hitherto the structural characters alone of the Ccelenterata have been 

 alluded to ; the development of these animals has yet to be taken into 

 consideration. The author then gave a condensed summary of the leading 

 results which have recently been obtained by those naturalists who have 

 directed their attention to the investigation of the life history of the 

 Ccelenterata; the researches of Sars, Siebold, Van Beneden, Dujardin, 

 Gegenbaur, Kolliker, Huxley, Strethill, "Wright, &c, being more es- 

 pecially particularized. He explained the nature of these valuable in- 

 vestigations, and the numerous and important advantages to science 

 which had already accrued therefrom ; the interesting questions to which 

 they gave rise ; and the relations, previously unsuspected, which they 

 had shown to exist between forms often widely separated from one 

 another. He also pointed out the gaps which yet remained to be filled 



