AOASSIZ. NATURAL HISTORY OF Till: [JUTTED STATES. 437 



plan of struct ure. namely, the radiate, common to the Polypes, Aca- 

 Icphs, and Eeliinoderms, and that all anatomical differences which 

 may exist between the two first of these classes, on the one hand, 

 and the Echinodennata, on the other, arc of a wholly subservient 

 character to the tact of their common radiation. — "There is no fea- 

 ture more striking in all these animals, in the Polyps and Acalcphs 

 on the one side and the Eeliinoderms on the other,' than the radiated 

 arrangement of their parts." Yet it may be doubted if even the 

 Eehinodermata are truly radiated. However, this is a point on whieh 

 at present we shall not dwell, but proceed at once to question the pro- 

 priety of applying the name Kadiata to many Ccelentcrate organisms. 

 The mode of attachment of the appendages in various genera of 

 Siphonophora is most assuredly not radiate.* Of the bilateral sym- 

 metry of the Actinoid Polypes and Ctenophora, Professor Aga^siz 

 himself reminds us. This, however, cannot be said to admit of more 

 than distant comparison with those indications of right and left 

 symmetry in certain Eeliinoderms, which have been pointed out by 

 J. Midler and Sars.f 



The resemblance, in outward aspect, between the adult forms of 

 the Ctenophora and the free-swimming larvae of most Eeliinoderms, 

 must be considered as wholly superficial and delusive in its character, 

 and as presenting in no wise that deep morphological significance 

 which Professor Agassiz would fain assign it. Elsewhere j he has 

 expressed his regret that Johannes Miiller, while prosecuting his 

 famous researches on the life-history of the Echinoderms, did not 

 avail himself of such excellent opportunities for tracing out, in com- 

 plete detail, the likeness between their larval forms and the Beroid 

 Medusa?. But the great anatomist of Berlin had too much real work 

 on his hands to find time for the pursuit of what to him must have 

 appeared no better than the vain shadow of a ehhnaera. Even in 

 the arrangement of its locomotive bands the young Ecliinoderm is 

 seen to contrast markedly with the Ctenophorid ; and in all other 

 essential features, such as histological differentiation of the body- 

 substance, structure of the digestive canal, and relation thereto of 

 the general cavity, the differences between the two organisms are 

 so great as almost to preclude the possibility of instituting a com- 

 parison between them. 



Nor have we read without surprise the statement of Professor 

 Agassiz, that the chambers between the radiating partitions of 

 Actinia and the radiating tubes of jEquorea correspond to the am- 

 bulacral vessels of the Eeliinoderms. The apparatus last mentioned 

 would appear to be without homologue among the members of the 

 Coelenterate sub-kingdom, while the radiating vessels of JEquorea, 



* See Huxley's Oceanic Hydrozoa, p. 8. 



t Consult the abstract of a recent memoir, by Sars, given in A. N. II., August 

 1861, p. 190. 



J Trans. Amer. Acad. May 1849, p. 366. 



