72 REPORT 1853. 



On the Mode of Growth of HaWchondria suberea. 

 Bi/ H. E. Strickland, M.A., F.R.S. 



This species of sponge, which is frequently ohtained by dredging, has long been 

 known for the peculiarity of its habitat. It is found investing the surface of old dead 

 univalve shells, which ot'ten present the appearance of being actually converted into, or 

 replaced by, the substance of the s.ponge ; for we find that the spiral cavity of the 

 shell is continued through the sponge for a considerable number of volutions, and is 

 always inhabited by some species of hermit crab. This has been explained by Dr. 

 Johnstone, in his ' History of British Sponges,' who supposes that the sponge by some 

 means dissolves, or absorbs, the larger volutions of the shell, and only leaves a small 

 portion of the apical volutions undestroyed. On carefully examining some specimens 

 which I lately dredged up, 1 found reason to believe that the sponge does not, as sup- 

 posed, remove any portion of the original shell, but merely prolongs its spiral volutions 

 Ijeyond their original extent. It is true that the enveloped portion of shell is often 

 corroded and imperfect; but this is owing to its having been in a dead and decayed 

 condition before the sponge began to grow : for in other cases the shell is sound, 

 full- sized, and with a perfect mouth ; and yet the spiral cavity is continued beyond it 

 for several volutions, through the substance of the sponge. In a specimen now pro- 

 duced is a perfect shell of the Nassa macula, a small species of univalve ; and yet the 

 sponge has grown to such an extent as to suggest the idea of having been modelled on 

 the much larger species, Na.isa reticulata. The continuation of the spiral cavity 

 through the sponge is evideritly due to the presence of the hermit crab, round whose 

 spiral body the sponge continues to grow, beyond the margin of the original shell. On 

 first noticing this peculiarity, it occurred to me that it might throw light on the very 

 remarkable spiral tube, filled with flint, which perforates certain fossil sponges from 

 tbe chalk, as described by Mr. Charlesworth in the Geological Section. It appears, 

 however, that the tubes in the fossil sponges do not taper, like those which in the 

 recent sponge are modelled on the continually enlarging body of the hermit crab, and 

 consequently the nature of the former structure still remains to be explained. 



On Preserving the Balance between Vegetable and Animal Organisms in 

 Sea Water. By Robert Warington. 

 The public were first indebted to Mr. "Warington for a statement of the conditions 

 in which animals could be kept in fresh water without changing the water. It is not 

 suflicient that there be plants alone ; but where the higher animals such as fish are kept, 

 it is necessary that some beings should exist which will feed on the decaying vege- 

 table matter. This desideratum is supplied by the various forms of phytophagous 

 MoUusca. The author's success with fresh water led him to try experiments with sea 

 water, and the results of his investigations were given in this paper. The most im- 

 portant fact established was, that marine aninials could be kept in sea water without 

 changing in the same manner as in fresh. The conditions of the existence of sea- 

 water creatures are, however, much more varied than those of fresh; hence the dif- 

 ficulty had been proportionally great in arriving at a successful issue. The nature of 

 the plants in the first place is a matter of importance. The author found that the 

 green sea-weeds answered better than the red or brown. In introducing animals they 

 should be healthy and uninjured. Those should not be put together which devour each 

 other. Ciabs, especially the common crab, are very destructive ; so are gobies, bleu- 

 nies, and rock-fish. The sea water should be kept of a proper gravity. It should be 

 about 1-026 at a temperature of 60°. Rain or distilled water should be added from 

 time to time to supply any loss. All dead animal or vegetable matter of any kind 

 phould be removed. 



