XCll 
THE VOYAGE OF H.M.S. CHALLENGEE. 
difference observed between tbe structure of the bud and that of the cortex of the parent 
sponge ; fig. 14, PL XLI V. represents a part of the tissue of one of the gemmules, and it 
would serve equally well for the outer part of the adult cortex. It is evident that there 
is room for fresh investigation of this subject. In a specimen of Tethya lyncurium, 
which I obtained at Eoscoff, the young gemmae still within the cortex of the parent were 
well displayed in thin slices of gold-chloride preparations, their position within the 
cortex is indicated in fig. 15 , PI. XLIIL, and one of them more highly magnified by 
fig. 16 of the same plate. 
5. CLASSIFICATION. 
Position of the Sponges in the Animal Kingdom. 
Before proceeding to classify the contents of the Tetractinellida, we must decide on 
its systematic value ; this involves a decision on the value of the group Spongiae, and 
in order to arrive at this, the closely connected question of the systematic position of the 
Sponges must be discussed. 
On this question there is profound disagreement of opinion among spongologists, as 
will appear from the following summary account. 
The Sponges are or have been regarded as — 
Protozoa — By Carter, Kent, and the late James Clark.^ 
Occupying a position intermediate to Protozoa and Metazoa — By Balfour. 
An independent phylum — By Butschli and Sollas (Parazoa, Sollas). 
Metazoa ; within this group regarded as — 
An independent phylum or special division — By Balfour, Sollas, Heider. 
Ccelentera. — By Leuckart, Haeckel, Marshall, Polejaeff, Schulze, von Lendenfeld, 
Ganin. Of those who hold this view, Schulze, Polejaeff, and Lendenfeld 
regard the Sponges as having branched off from the rest of the Ccelentera 
at a very early stage, Marshall (as at one time Anton Dohrn) regards them 
as degenerate Ccelentera, which, according to Marshall, at one time possessed 
tentacles, nematocysts, and mesenteric pouches. 
That the Sponges cannot be regarded as Protozoa seems to have become a settled 
opinion, with which all the known facts are in agreement. The same can hardly be said 
of the view which regards them as degenerate Ccelentera, and which rests chiefly on the 
radiate symmetry presented by the canal-system in two or three species ; till it can be 
shown that this symmetry in those cases in which it is definitely expressed is a primitive 
and not a secondarily acquired character, it cannot be credited with any special 
significance. As to its being primitive, all the facts so far as they are known to me are 
definitely opposed to such a view, 
1 Amer , Journ . Sci . and Arts , ser. 2, vol. xviii. p. 320, 1866. 
