[ 194 



ADDITIONS AND CORRECTIONS. 



The Siliceous Spicula, p. 8, 89. 

 From the recent researches of Mr Bowerbank we learn, that 

 the forms of the siliceous Spicula are more diversified than was 

 previously believed ; and that they are, perhaps, even more va- 

 ried than those of the calcareous sponges. The triradiate form 

 is certainly not peculiar to the latter. 



The Circulation of the Sponge, p. 14. 

 Mr Hogg has informed me, that he has also seen the circu- 

 lation of a marine sponge in Halichondria panicea. He could 

 not detect any evidence of an influent current ; neither did he 

 detect, with the magnifier he used, any circulation whatever in 

 Grantia foliacea. I am not aware that Mr Hogg has abandon- 

 ed his opinion of the circulation being, as it were, alien and ac- 

 cidental, and dependent on nestling animals. 



The Propagation of Sponges, p. 18. 

 Mr Bowerbank's researches seemingly tend to prove the cor- 

 rectness of Professor Grant's description of the gemmules of the 

 sponge, although he has not actually seen the cilia in those of any 

 recent species which have yet come under his observation. Some 

 observations made by Mr Bowerbank on fossil sponges lead to 

 a suspicion, that, in some, there may have been an appropriate 

 organ for the production of the gemmules. 



Fossil Sponges, p. 22. 

 In explanation of these, I refer the reader to a very interest- 

 ing paper by J. S. Bowerbank, " On the Siliceous Bodies of the 

 Chalk, Greensands, and Oolites," published in the sixth volume 

 of the Transactions of the Geological Society of London, p. 181. 

 Lond. 1841. 



