442 Zoological Classification, 



In the Articulates we can readily distinguish four classes, cor- 

 responding to those of the Vertebrates : 1st. The arachnidans, 

 with high sensorium and intelligence, and no metamorphosis, and 

 representing the mammalia ; 2nd. The insects, corresponding to 

 the birds ; 3rd. The crustaceans, corresponding to the reptiles ; 

 ith. The worms, corresponding to the fishes. 



In the MolluskSy we have : 1st. Cephaiopods, corresponding to 

 arachnidans and mammals ; 2nd. Pteropods and gasteropods, cor- 

 responding to birds and insects ; 3rd. Lamellibranchiates, corres- 

 ponding to reptiles and crustaceans; and lastly, the tunicates, 

 brachiopods, and bryozoa present an enlarged representation of 

 the fishes. 



If the Radiates really constitute a natural group, they should 

 conform to this general plan. Here we have : 1st. Echinoderms, 

 which constitute a class, and the highest of the province ; 2nd. 

 Acalephs,the specially locomotive class; 3rd. Anthozoa, or acti- 

 nozoa, or polyps, the vegetative class ; and lastly, protozoa, with 

 the lowest endowments in respect to internal parts and sensorium. 



Our Protozoa are thus required in order to bring the Radiates 

 into harmony with the other provinces ; and it seems plain that 

 the group is much nearer its true place as a class, than as a pro- 

 vince. The question still remains, whether some of the Protozoa 

 might not be more naturally placed at the base of other sub-king- 

 doms than those of the Radiates ^ as, for instance, the Vorticellce, 

 with the Bryozoa; Gregarinida and some Infusoria with the 

 worms. It seems likely that this may eventually be done ; and 

 that just as the Bryozoa^ Entozoa^ and Rotifers are now gene- 

 rally separated from Radiates, a more nice analysis of the cha- 

 racters of the more aberrant Protozoa, may enable some of them 

 to be separated from that group. 



As an additional evidence of the correctness of the view above 

 stated, I may remark that the divisions of Protozoa proposed by 

 Carpenter have much more of the character of orders than of 

 classes, in this respect that they imply rather gradations of rank 

 than different ways and means of execution. Another proof is 

 offered by the strong resemblance of many Protozoa to the embry- 

 onic states of true members of the province Radiata. 



With respect to the Coelenterata, the case is still more clear. 

 The structural and embryonic evidence given by Agassiz, in his 

 last and the preceding volume, amply prove the aflinity of these 



