NORTH AIEKICAN ACALEPHJE. 



OEBEE CTENOrilOR/E ESCH. 



Clrnopliorcc Escn. Syst. der Acalcphen, p. 20. 1820. 

 Ctenoplione GKGEXBAUK. Archiv. f. Natur^., 1856. I, p. 1G3. 

 Ctfnophone Ac; ASS. 18GO. Cont. Nat. Hist. U. S., III. p. 289. I860. 

 Ciliof/radex BLAINV. Man. d'Actin., p. 143. 1830. 

 Beroides LESS. Zoopb. Acal., p. 01. 1843. 



The affinities of the Ctenophorai have become one of the most fertile 

 topics of discussion among recent investigators. Vogt, following Quoy, 

 removes them from the Acalephs altogether. Huxley places them in 

 close proximity to Polyps. Clark has made a special class of them, 

 equivalent to Echinoderms, while Milne Edwards and Agassiz, after a 

 careful revision of the whole subject, have followed Cuvier and Esch- 

 scholtz, and retained them as an order of Acalephae. These various views 

 of the true relations of the Ctenophorse are based upon very different 

 grounds, and are urged with more or less force in accordance with the 

 degree of importance attached by investigators to the details of struc- 

 ture upon which they separate the Ctenophorre from the Acalepho?, and 

 refer them to other classes of the Animal Kingdom ; the apparent bilat- 

 erality so strongly developed in some of the families (as Cestum, Bolina, 

 and Mertensia) being urged by Vogt as the principal ground for re- 

 moving them from Acalephs, and associating them with the Mollusks ; 

 while Huxley places them with Polyps on the ground of the special 

 structure of their digestive cavity ; and Clark simply states his belief 

 in their separation as a class, without furnishing us any proofs. We 

 are able to throw new light on this question by a series of facts derived 

 from their embryological development, hitherto unnoticed. As the ob- 

 servations of Dujardin on the development of Coryne gave us the key 

 which led to the ultimate separation of the Hydroids from the Polyps, 

 so I hope to be able to show that the development of the Ctenophorse 

 gives us a true insight into the disputed affinities of these animals. 



Before the publication of the valuable observations of McCrady on the 

 development of a species of Bolina, little was known of their embryology 

 except the mere fact, derived from the few casual observations of Miiller, 

 Wright, Boeck, and Price, that the Ctenophoree were probably all repro- 



