LITEKATTTRE OF THE STJB-EXNGDOM CCELENTEEATA. 419 



Badiata, as restricted in recent works, includes but three classes : 10 — 



1. ECHIXODEEMATA. 



2. ACALEPH^!. 



3. Polypi. 



It has been shown, however, by Trey and Leuckart 11 that the 

 Polypi and Acalephse, while possessing in common a plan of structure 

 peculiar to themselves, differ, on the other hand, both as to type and 

 grade of organization, from the members of the group Ecliinoclermata. 

 They have, therefore, proposed to associate the two former classes in 

 a separate sub-kingdom, under the name of Ccelenterata, 12 i.e., animals 

 having a well marked body-cavity, freely communicating with that 

 portion of it which may be concerned in the discharge of the digestive 

 functions. The propriety of this arrangement has been acknowledged 

 by some of our most trustworthy living observers. 



Thus far with reference to the sub-kingdom Ccelenterata as a 

 whole ; next, as to its classes and orders. It has been said that this 

 group includes the two classes termed Acalephse and Polypi in the 

 system of Cuvier, the Sponges and Polyzoa being no longer associated 

 with the latter. 



Cuvier thus divided the Acalephse and Polypi into orders : — 



Les Acalephes. Les Polypes. 



Ordre 1. A. Simples. Ordre 1. P. Ckaenus. 



Ordre 2. A. Htdrostatiques. Ordre 2. P. Gelatlweiix. 



Ordre 3. P. a Polypiees. 



Pew zoologists, however, adopted these divisions. Eschscholtz, 13 

 in 1829, suggested a re- distribution of the Acalephae which soon met 

 with very general approval, and, in many of its features, is still 



10 For example, Edward Forbes, so far back as 1840, recognizes the propriety of 

 employing the tenn Radiata in the above limited sense. See the introduction to his 

 History of British Star-fishes. 



11 Op. s. cit., pp. 37-8. 



12 What then, it may be asked, becomes of the class Echinodermata ? To this 

 question the answer is, that not less than four different views are at present main- 

 tained as to the systematic position of these animals : — 



1. That of those naturalists who refuse to acknowledge the Ccelenterata, and 

 regard the Echinodermata as a class of the sub-kingdom Radiata. 



2. That of R. Leuckart, Gegenbaur, J. V. Carus, and others, who place the 

 Echinodermata in a sub-kingdom by themselves) distinct from the sub-kingdom Cce- 

 lenterata. 



3. The intermediate view of Milne Edwards who, retaining the old group of 

 Radiata, considers the Echinodermata and Ccelenterata as constituting its two pri- 

 mary, equivalent sub-divisions. 



4. Lastly, it has been proposed by Huxley, who acknowledges the sub-kingdom 

 Coelenterata, to refer the Echinodermata, as a class, to the Annullose sub-kingdom, 

 with certain forms of which (the Intestina and Rotifera of Cuvier) they constitute a 

 very natural assemblage, best known under the name of Annulloida. 



13 System der Acalcphen, Berlin, 1829. 



