108 ESSAY ON CLASSIFICATION. 



investigated, and some types of this branch are among 

 the very best known in the animal kingdom. The natural 

 limits of the branch itself appear, however, somewhat 

 doubtful. I hold that it must include theBryozoa, 1 which 

 lead gradually through the Brachiopods 2 and Tunicata to 

 the ordinary Acephala, and I would add that I have satis- 

 fied myself of the propriety of uniting the Vorticellidse 

 with Bryozoa. On the other hand, the Cephalopods can 

 never be separated from the Mollusks proper, as a distinct 

 branch ; and the partial segmentation of their yolk no 

 more affords a ground for their separation, than the total 

 segmentation of the yolk of Mammalia would justify their 

 separation from the other Vertebrata. Moreover, Cepha- 

 lopods are, in all the details of their structure, homologous 

 with the other Mollusks. The Tunicata are particularly 

 interesting, inasmuch as the simple Ascidians have pedun- 

 culated young, which exhibit the most striking resemblance 

 to Boltenia, and form, at the same time, a connecting link 

 with the compound Ascidians. 3 The development of the 



1 ALLMAN, (G. J.,) On the Present (F.,) Infusionsthiere auf ihre Ent- 



State of our Knowledge of the Fresh wickelungsgeschichte untersucht ; 



Water Polyzoa, Proc. Brit. Asso. Adv. Leipzig, 1854, 1 vol. 4to. fig. 



Sc., 20th Meet. ; Edinburgh, 1850, p. FRANTZIUS, (AL. v.,) Analecta ad 



305. Proc. Irish Ac. 1850, vol. 4, p. Ophrydii versatilis historian! natu- 



470. Ibid., 1853, vol. 5, p. 11. Mo- ralem, Vratislav, 1849. LACHMANN, 



nograph of the Fresh-water Polyzoa, (C. F. J.,) Ueber die Organization der 



Ray Soc. VAN BENEDEN (P. I.,) Infusorien, besonders der Vorticellen, 



Recherches sur 1'Anatoinie, la phy- Miiller's Arch., 1856, p. 340. Having 



siologie et le developpement des Bry- satisfied myself that the Vorticellidje 



ozoaires qui habitent la cote d'Os- are Bryozoa, I would also refer here 



tende, Nouv. Mem. Ac. Brux., 1845, to all the works on Infusoria in 



vol. 18. DUMORTIER, (B.C.,) et VAN- which these animals are considered. 



BENEDEN, (P. J.) Histoire naturelle 2 I see, from a short remark of 



des Polypes composes d'eau douce, Leuckart, Zeitsch. f. wiss. Zool., vol. 



Mem. Ac. Brux., 1850, vol. 16, 4to. 7, suppl., p. 115, that he also has per- 



fig. HINCKS, (Tn.,) Notes on British ceived the close relationship which 



Zoophytes, with Descriptions of some exists between Brachiopods and Bry- 



New Species, Ann. and Mag. Nat. ozoa. See also HANCOCK (ALB.), On 



Hist., 2d ser., 1851, vol. 8, p. 353. the Organization of the Brachiopoda, 



EHRENBERG, (C. G.,) Die Infusions- Proc. Roy. Soc. ; London, 1857, p. 



thiere als vollkornrnene Organismeu, 463. 



Leipzig, 1838, 2 vols. fol. fig. STEIN, 3 SAVIGNY, (J. C.,) Memoires sur 



