58 ACALEPIIS IN GENERAL. Part I. 



Hydi'okls, a fourtli : unless we separate at onee the Sertularians with their horny 

 stem and l)ell as a sub-order, distinct from the Tubuhirians, with their soft Hydroids, 

 which seems to l)e the more appropriate course. Diph3'ida? and Physophorida? may 

 require to Ijc subdivided in tlie same way. 



Now tliat the investigations of Oilers, Leuckart, Quatretages, and Huxley, have 

 made us as fully acquainted with the structure of Pliysalia as we are with that 

 of the other Siphonophora", it is hardly wortli while to recall the opinion of 

 DeBlainville upon these animals, as it is evident from his description, that he could 

 never have entertained such views about them, had he ever had an opportunity 

 of studying them for himself DeBlainville considered Physalia as a single animal, 

 which he referred to the type of Mollusks in connection with the Ileteropod 

 Gasteropods, considering the crest of the Ijladder of Physalia, as its foot, similar 

 to that of these Gasteropods, and the pendent ajipendages as gill-like organs similar 

 to those of the Dorsibranchiate, while he describes the opening of the Ijladder as 

 their mouth. But I mj'self have hail repeated opportunities for examining Physalia 

 alive, and this examination has left no doubt on my mind that it constitutes a 

 comj^ound community of a great variety of individuals, i)resenting all the characters 

 of true Hydi'oids. 



It is important here to remark, that this great discrepancy in the ojiiuions 

 expressed respecting the affinities of these animals was in a measiu'e owing, either 

 to an insufficient acquaintance with their true structure, as was no doubt the case 

 with Blainville when he referred Physalia. to the type of Mollusks, and with Vogt 

 when he referred the Ctenophoraj to the same tyjie, or to a want of familiarity 

 with the other objects associated with them, as is no doid^t the case with the 

 German authors, who, from a want of ojjport unity of examining Corals nYixo, have 

 so generally vmited the Hydroids and Siphonophora^ with the Polyjjs. It is a 

 remarkable circumstance, that the naturalists who have known the PolyjJS best, as 

 Milne-Edwards and Dana, never thought of associating the Siphonophora- with them, 

 though they were ecpially acquainted with Ijoth, and though we owe to Milne- 

 Edwards in })articular, some of the most minute investigations extant upon the 

 Siphonoj)hora'. As to the Hydroids, though they are associated by Milne-Edwards 

 with the Polyps, he considers them as forming by themselves a natural division 

 in that class, cocfpial with the Halcyonoids and Actinoids ; while Dana, goes one 

 step farther in the right direction, by uniting the Hakyonoids and Actinoids in 

 one natural division, to which he opposes the Hydroids as another di\ision of 

 equal value. But even this ])ositiou Dana has lately abandoned, and he now" 

 unites the Hydroids with the true Acalephs; so that it may be truly said, that, 

 in proportion as oiu- knowledge of the Siphonophora>, the Hydroids, and the Polyps, 

 has gradually advanced, naturalists have perceived more and more distinctly the 



