244 Agas&iz' Contributions to the 



Including in this last the Acrita, or those in which a nervous sys- 

 tem, existent no doubt, has not yet been distinctly traced. 



Agassiz, as we have seen, prefers to take a more general view 

 of the plan of structure as a whole, though accepting the four 

 branches of Cuvier. We confess that we entertain doubts whether 

 this is not, as compared with the position of Owen, a backward 

 step. We might point, for example, to undoubted Radiata even 

 among the Echinodermata and Acalephae, in which the general 

 radiated structure does not exist, while the type of nervous 

 system does. On the other hand, the separation of the Bryozoa, 

 the Rotifera and the Eutozoa from the Radiates, now so generally 

 accepted, appears to us very likely to be condemned in the future 

 progress of Zoology, as an error caused by want of attention to 

 dominant structures, as compared with those which pertain to 

 merely vegetative life and accidents of existence.* 



Before leaving this subject of the division of Animals into four 

 great, branches, we would pause to insist on the fact, that ^ bile, 

 as our auihor very properly insists, this division does not depend 

 on gradation of rank or complexity of structure", it is still insepa- 

 rably connected with these, just as in art, certain styles are con- 

 nected with higher and others with lower works. The Vertebrate 

 in no form sinks so low as the Invertebrate; and though the 

 Articulates and Molluscs may be regarded as parallel series, both 

 are higher on the whole than the Radiates and lower than the 

 Vertebrates. These differences are not arbitrary, but apparently 

 based on the inherent capabilities of the types themselves. 



* As an illustration of the reasons for doubt on this subject, we may- 

 point to the fact that in Allman's recent able monograph, he admits the 

 difficulty of establishing the homology of the nervous systems in Bryozoa 

 and Tunicates. In short, he finds affinities in the accessories, but fails 

 to find them, or finds them only obscurely, in the essential structures per- 

 taining to sensation and voluntary motion. Huxley, who differs mate- 

 rially from Airman in his explanation of these supposed homologies, 

 finds the same difficulty. On the other hand, some marine worms affect 

 the general aspect of Bryozoa ; and we know from personal observation 

 as well as from the statements in the work now before us, that the 

 Vorticellidse, with no good claim to be regarded as Molluscs, are little 

 else than minute Bryozoa. In our view the radiates should be regarded 

 as not strictly a distinct branch, but as a sort of root-stock of the animal 

 kingdom, approaching in many points in its plans of structure to the 

 plant, and in other points uniting itself closely with the basis of the 

 Molluscous and Articulate branches. 



