FORM OF A SPONGE 315 



This sponge was gathered on May 20, and from Vosmaer 

 (' Mitth. Z. S. Neapel ', v, pp. 486, 487) was probably only a 

 month old, during w^hich time its volume and the volume of 

 its delivery must be supposed to have increased by some 

 40 per cent, every day in geometrical progression. Then the 

 total amount of water passed during its whole life would be the 

 equivalent of 3-J- days of its final delivery, and it would have 

 extracted food from a total weight of 80 kg. of water. 



By weighing the preserved sponge alternately in alcohol 

 and water I found the total volume 0^31 c.cm., weight 0^59 gm., 

 . '. sp. gr. 1^9. Allowing 2^5 for the sp. gr. of the spicules and 

 1-4 for that of the dry protoplasm, this gives 



Total Volume. Dry Weight. 



Spicules of Leucandra aspera (Text-fig. 1) 

 Protoplasm ....... 



•31 -59 



Therefore from 80 kg. of water the sponge abstracted a total 

 weight of 0^38 gm. of carbonate of lime, or 0^00.5 gm. per kg., 

 or about one-third of the amount of carbonate of lime which 

 can be dissolved in pure water free from carbonic acid, and 

 about one-twelfth of the total lime in an average sample of 

 sea-water. If we suppose the sponge's life to have been longer, 

 or the osculum to have been more dilated (Note 6), the per- 

 centage proportion of lime extracted is proportionately less. 



Note 4. Fan-shaped Sponges. 



There is a possibility that these, like the Hexactinelhds, are 

 found always in a permanent current, on which they depend 

 for subsistence. 



After this paper was read at the British Association, Sir W. 

 Herdman kindly informed me that in the deeps off Scotland 

 (where the sponges were found from the figures of which 

 Text-fig. 11 was made) there are many places where the 

 current sets only one way. And Professor Stanley Gardiner 

 added that in 30 fathoms off the Seychelles (where the sponge 



