75 



Other authors have written on these subjects since the publication 

 of Dr. Grant's papers, but none in so lucid and so effectual a manner: 

 and unfortunately one of the most celebrated of these has done much 

 more to retard than to advance our knowledge of these subjects. I 

 allude to Raspail, who, in his papers on Spongillafriabilis, published 

 in "the ' Memoires de la Societe d'Histoire Naturelle,' 1828, labours 

 very hard to prove Dr. Grant in error, in having described the spicula 

 of Spongilla, and some other sponges treated of in his papers in the 

 1 Edinburgh Philosophical Journal,' as cylindrical bodies ; and endea- 

 vours to prove them to be vegetable crystals or raphides, and of a 

 hexagonal form : and figures them as such in Plate xxii. figs. 5 and 6 

 of the Memoires, as seen without immersion in water, while at fig. 4 a 

 spiculum immersed in water is represented, which presents precisely 

 the natural appearance, and agrees exactly with the description of Dr. 

 Grant. The singular perversion of Raspail's ideas on this subject, 

 can only be accounted for on the supposition that he did not take in- 

 to account the great amount of spherical aberration that inevitably 

 ensues when the rays of light pass through transparent cylindrical bo- 

 dies of high refractive powers. From the great celebrity of Raspail 

 as an observer and a writer, it becomes the more necessary that these 

 errors should be noted : and it is but justice to Dr. Grant to state 

 that I have followed him to a considerable extent in his observations 

 on Spongillafriabilis and many other species of which he has treated, 

 and I can bear testimony to the truth, accuracy, and acuteness of 

 observation displayed in his laborious and valuable contributions to 

 science. 



