172 Dr. J. E. Gray on 8;ponges. 



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 Gummineae are allied to Halichondrise 

 rather than to Ceratospongise. 



Dr. W. Thomson objects to my separation of the Sponges 

 into Malacosporae and Chlamydosporse. 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 Geodiadge and Spongilladse ; 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 skeleton of Spongilla is doubtless very like that of 

 Halichondria^ or rather Isodictyon^ as Dr. Thomson says after 

 Dr. Bowerbank. The ovisacs of many Isodictya are known, 

 and they are all membranaceous. 



Both Geodiada3 and Spongilladse 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 Placospongise, 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 natui-e as we can discover, is to search for 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 

 appeared 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 " ^. speciosum as 

 a variety grown under peculiar circumstances, and the shorts. 

 corhicula with the netted lid as the normal form" of the spe- 

 cies. Another is, surely, that Dr. Schultz has proposed to 

 unite Ewplectella and Hyalonema into one family, called 

 Lophospongige (see Arch. micr. Anat. iii. 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 

 siliceous 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 EuplecteUa and Hyalonema. 



