572 DR. R. VON LENDENFELD ON THE SYSTEMATIC [Deec. 21, 
at. The one I propose in this paper, which is similar to that of 
Vosmaer, is certainly very far from being as perfect as I would like 
to make it; but I think that at all events it is much more likely to 
express the relationship of Sponges in a correct manner than any 
other existing arrangement. 
The subclass Silicea minus the order Hexactinellida comprises the 
Sponges with a skeleton composed of tetraxial spicules (the Tetrac- 
tinellida and Lithistide of Marshall and other authors), the Sponges 
with monaxial spicules (the Monactinellida of Zittel and other 
authors), the Sponges with a horny skeleton and without spicules in 
the supporting skeleton (the Ceraospongiz or Keratosa of many 
authors), and, finally, the Sponges without any supporting skeleton 
at all (the Myxospongize of Hiickel). 
At first sight all these forms appear connected with each other in 
every direction by transitional forms to such an extent that it seems 
hopeless to bring order into this chaotic mass. A careful investi- 
gation of many forms shows that all the familiar groups Tetracti- 
nellida, Lithistidse, Monactinellida, Ceraospongiee, and Myxospongiz 
run into each other at every point. If one, however, for years 
endeavours to find some constancy in the varying characters of any 
chaotic mass of this kind, he at last generally arrives at an idea which 
seems clear enough when once grasped. And then one only wonders 
how it was that it had not been conceived a long time ago. So it 
was also in this case. I found that all these Sponges could be very 
naturally divided into ¢wo Orders—the above-mentioned Chondro- 
spongie and Cornacuspongie, the first of which comprises the 
Lithistids, Tetractinellida, and portions of the Monactinellida, together 
with most Myxospongie ; whilst the second contains all the Cerao- 
spongiz, and the remainder of the Monactinellids and Myxo- 
spongiz. 
We find that the ground-substance, the mesodermal intercellular 
substance or Mesogleea, as it is variously termed, is more or less hard 
and cartilage-like in the Chondrospongiz, and that in these the spi- 
cules remain isolated. The spicules are either tetraxon or tylostyles, 
less frequently styles. The monaxon spicules are monact, thereby 
indicating their closer affinity with the tetraxon spicules. The 
necessary toughness is given to these Sponges not by a cementing of 
the spicules, but by a hardening of the ground-substance. In some 
the spicules disappear altogether, as in Oscarella, which is an aske- 
letous form of Plakina, and in Chondrosia, which is an askeletous 
sponge belonging to the Tethya group. 
In the Cornacuspongiz, on tbe other hand, there is no tendency 
towards a hardening of the ground-substance discernible. The 
ground-substance remains soft and gelatinous, and the necessary 
toughness is given to the sponge by the formation of a substance not 
found in other Sponges, which cements the spicules together. This 
substance is chemically and physically comparable to silk or horn, 
and is known as Spongin. 
The spongin may become very voluminous and the spicules 
scarce and small. ‘They may finally disappear altogether, and then 
