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 Ccelenterate 
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 Coelenterata 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 Coelenterata 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. 
Crass: SPONGLA. 
Order I. Myxosponaim, Haeckel. 
> LI. Ceratosroncim, Bronn.” 
Sub-Order. 
1. Monactinellide, Zittel. 
2. Tetractinellidss, Marshall. 
3. Lithistide, Os. Schmidt. 
4. Hexactinellide, Os. Schmidt. 
5. Octactinellide, Hinde. 
6. Heteractinellide, Hinde. 
», LV. Cancisronarm, Blainville. 
» LI. Sinicitsponaim 
