OF THE NATURE OF SPONGES. 43 



from their chemical composition is fallacious, ^' for most 

 of the marine plants emit when burnt an odour analogous 

 to that of animal substances, which appears to originate in 

 the simplicity of their structure and their habitation." He 

 was led to the conviction of sponges being plants by observ- 

 ing that the fresh-water sort contained myriads of minute 

 green granules, v.hich, when shaken from the common mass, 

 were observed to grow and develope entirely after the man- 

 ner of vegetables. The opinion had been entertained by 

 Mr Gray for some years, for sponges are introduced into 

 the " Natural Arrangement of British Plants," published 

 in 1821, by Samuel Frederick Gray, and in the compila- 

 tion of which the celebrated zoologist is believed to have 

 assisted. 



Mr Gray's attention was also particularly drawn to the 

 " internal structm'e" of sponges, but his generalizations 

 were hasty and erroneous, for he evidently means us to in- 

 fer from his statement that the fibres of all sponges are 

 composed of agglutinated spicula ; and of the natm'e and 

 variety of these he appears to have been ignorant. He 

 says — " On examining the sponges which have come un- 

 der our observation, (not a small number of species), they 

 all appear to be essentially formed after the same manner, 

 that is to say, of longitudinally placed transparent fusiform 

 spicida, wliich vary considerably like the species, in size 

 and in the closeness of their connection, for in those spe- 

 cies that appear to be fibrous, the fibres are composed of 

 spicula united together by a cartilaginous substiince : and 

 the Spongia tomentosa, which is the one said to be formed 

 of bundles of spicula by Ellis, if it be carefully examined, 

 bv breaking it from the centre of the ba^e to Ihr- rirnun- 



