CLASSIFICATION. 85 



Systematic Position and Classification. 



The position of Sponges in the animal kingdom may now be said to be decided 

 generally in favour of their belonging to the Metazoa, but there is not the same 

 unanimity of opinion as to whether they should be included in the Coelenterate 

 type or placed independently as the lowest division of the Metazoa. It is a 

 question which can only be decided by a consideration of the embryological 

 development and the soft structures of the organism, and no light whatever is 

 thrown on it by the fossil forms. So long since as 1867, Sponges were regarded 

 as Ccelenterata by Leuckart, and this view has gradually been accepted by most 

 authorities on the subject till within a recent period ; but at the present time the 

 opinion that they represent a type distinct from the Ccelenterata seems to be 

 most in favour. Similar differences of opinion also exist with respect to the 

 classification of existing Sponges, and nearly every recent author on the subject 

 propounds a distinct system, differing alike in the main as well as in the subordi- 

 nate divisions from those previously advanced. Attempts have even lately been 

 made to arrange the Sponges according to the characters of their soft structures, 

 but it need hardly be said that any system on this basis would be entirely useless 

 for fossil forms, in which only the mineral portions of the skeleton are available 

 for purposes of classification. 



As regards the classification of fossil Sponges, it seems scarcely necessary to 

 mention the various systems in use previous to that brought forward by Professor 

 Zittel, since they are now regarded as obsolete, and possess a mere historical 

 interest. The main features of Zittel' s classification, which I propose to adopt 

 with some modifications, depend on the characters of the skeletal elements of the 

 organism. The following list shows the leading divisions. 



Class: SPONGLE. 

 Order I. Myxospongle, HaecJcel. 

 „ II. Ceratospongle, Bronn. 



Sub-Order. 



1. Monactinellidse, Zittel. 



2. TetractinellidaB, Marshall. 

 , 3. Lithistidse, Os. Schmidt. 



4. Hexactinellidae, Os. Schmidt. 



5. OctactinellidaB, Hinde. 



6. Heteractinellidae, Hinde. 

 IV. Caloispongi^, Blainville. 



