172 Dr. J. E. Gray on Sponges. 
bank has shown that Halisarca contains spicules. If Dr. W. 
Thomson’s arrangement had been founded on the examination 
of specimens rather than on the characters in books, he would 
have found that the Gummines are allied to Halichondrie 
rather than to Ceratospongie. 
Dr. W. Thomson objects to my separation of the Sponges 
into Malacospore and Chlamydospore. The spores of many 
Sponges are not known, as he observes; but, though we may 
not know the structure of the spores of many species and ge- 
nera, we do know that they have not ovisacs or spores like 
the Geodiade and Spongillade; for if they had, we should 
have observed them, as it is almost impossible to examine a 
fragment of a Sponge of either of those families without seeing 
them. The skelator of Spongilla is doubtless very like that of 
Halichondria, or rather Lsodictyon, as Dr. Thomson says after 
Dr. Bowerbank. The ovisacs of many Jsodictya are known, 
and they are all membranaceous. 
Both Geodiade and Spongillade are well defined recognized 
groups: the latter lives only in fresh water, and is green, all 
the other Sponges being marine and never green. And Dr. 
Thomson must regard the solidified ovisac as a good character, © 
or I do not see how otherwise he can arrange the solid calca- 
ceous Placospongie, which certainly have no bark distinguish- 
able from the axis, such as characterizes his corticata. 
I believe the proper way to form a natural system, or one 
as near nature as we can discover, is to search br some cha- 
racter that is common to a large number of the species, and 
when one is found, if the group appears a natural one, to 
use that character for the group, however trivial it may have 
speared to our preconceived notions. And this is the course - 
I followed when studying the Sponges; and the result of that 
study was the belief that the nature of the ovisac does form a 
good character to separate the Sponges into two groups. 
The “ fatal fascinations of the beauties’ do not seem to have 
come to an end; and I think I may add to the instances re- 
corded by Dr. W. Thomson that he regards ‘‘ A. speciosum as 
a variety grown under peculiar circumstances, and the short A. 
corbicula with the netted lid as the normal form” of the spe- 
cies. Another is, surely, that Dr. Schultz has proposed to 
unite LHuplectella and Hyalonema into one family, called 
Lophospongie (see Arch. micr. Anat. ili. 212)! It is asto- 
nishing that such an anatomist should regard Hyalonema as a 
Sponge, as it has not one character of the class, except its 
whoaca spicules; and even if it were a Sponge, no. two ge- 
nera of the same class could be more unlike in structure and 
form than Huplectella and Hyalonema. : 
