OF THE MOLLUSCOIDA AND CGELENTERATA. 



519 



cilia circulating a corpusculated fluid, but also contains the reproductive organs. 

 Finally, the tentacula in the Ccehnterata are in most cases both prehensile and 

 respiratory, while in many they are also locomotive. 



The accompanying series of diagrams will show more distinctly the relation- 

 ship of the various organs and parts in the five groups so imperfectly glanced at 

 above. 



A. B. C. 



D. 



E, 



F. 



G. 



A. An Ascidian. 



B. A Polyzoon. 



C. Cydippe. 



D. Actinise, fixed and free. 



10-— < 



E. Tubularia. 



F. Clava. 



G. Hydra. 



The numerals have a corresponding signification in all the figures. 



1. The outer oral, or brancWal tentacula of Tunicata, which do not appear again in any of the 



inferior types. 



2. The outer mouth or branchial opening of Tunicata only to be represented theoretically, by the 



conjoined summits of the tentacula of Polyzoa. 



3. The branchial cliamber or respiratory pharynx of Tunicata^ to which the tentacula of Polyzoa 



and the ciliated bands of Cydippe may offer an equivalent; being thus pharyngeal in the 

 first, oral in the second, and somatic in the last. It is, moreover, altogether absent in the 

 other sections of Coelenterata. 



4. The inner or oesophageal opening of Tunicata, and the proper mouth of Polyzoa, Ctenophora, 



and Actinozoa. 



5. Pyloric orifice of the stomach, leading into a closed intestine in Tunicata and Polyzoa ; and 



into an intestine communicating with the somatic cavity in Ctenophora ; and solely into the 

 somatic cavity in the Actinozoa. Probably, also, in the everted state forming the oral orifice 

 in Hydrozoa. 



6. Anal extremity of the intestine in Molluscoida and Ctenophora. 



7. Position of the nervous ganglion in the same. 



8. The oral tentacula in Actinozoa, probably equivalent to the outer or somatic tentacula of the 



Hydrozoa, always occurring on the outer or proximal side of the reproductive organs. 



9. The oral tentacula of Hydrozoa, always on the distal side of the young gemmules. In accord- 



ance with the views here expressed, it may be assumed that the inner circle of Tubularia is 

 homologous with the single series of Hydra, &c. 



Regarding Cydijype as holding a middle position in the foregoing series, the 



VOL. XXIII. PAET II. 7 B 



