CLASSIFICATION OF ANIMALS. 199 



ing to their structure and development, is it not remarkable, does it 

 not indicate the maintenance of the same plan throughout the crea- 

 tion, "vvhen we find chambered shells, so abundant throughout the 

 ancient geological formations, and belemnites, the analogues of the 

 cuttle-fish, beginning late in the secondary epoch in the lias ; whilst 

 fossil argonauts do not occur before the tertiary times ? So that 

 we might almost conclude, that in this class the order of succession 

 of their fossil types is a safer guide for our classification, than ana- 

 tomical investigation. 



In the class of Acephala the low position of brachiopods in the 

 order of appearance in time, as well as in our estimation of their 

 structural standing, is another striking instance of the correspondence 

 between the order of geological succession and the gradation in struc- 

 ture. I may add as a link for farther inference, that I have seen 

 embryonic cyclas attached by a byssus to the gills of the mother. 



There is perhaps no department in which we may expect more 

 important results for methodical arrangement from embryological 

 researches than that of the Radiata. Let us only consider the met- 

 amorphosis of the MedusEB, their first polyp-like condition, their 

 division and the final transformation of their stem into several distinct 

 individuals, exemplifying in a higher sphere the growth of compound 

 Polypi, where the successive bvids remain united upon a common 

 stock. Let us remember the free Comatula growing from the egg 

 upon a Crinoid-like stem ; let us then remember, that there are ani- 

 mals of that class, which preserve throughout life this articulated 

 support, and remind us of corals even in the highest class of Radiata ; 

 let us farther know, that even the arrangement of plates in those 

 Crinoids agree in some respects with the first formed calcareous 

 granules in free moving starfishes ; let us finally and above all here 

 remember, that those Crinoids with stems are only Echinoderms of 

 earlier ages, which die out gradually, to be replaced by new and free 

 forms, and there will not be the slightest doubt left in our minds, that 

 besides the structure, there is no safer guide to the understanding of 

 the plan of the creation of the animal kingdom, as it has been in 

 former ages and as it is in our days, than embryological and palaeon- 

 tological researches. 



The internal arrangement of these classes as I now conceive it, would 



