2 ANATOMY AND PHYSIOLOGT 



duction to the study of the Spongiadse, as an excellent 

 preparation for the investigation of the British species. 



From the researches of Dr. Johnston, detailed in Chapter 

 III, " The Discovery of British Species," it appears that the 

 first British sponge recorded was by Mathias de I'Obel, in 

 1616. Ellis, in his 'History of British Corallines,' 1755, 

 described two species, and in his 'Zoophytes,' 1786, edited 

 by Solander, the number is increased to seven ; other spe- 

 cies were described by Professor Jameson and Mr. James 

 Sowerby; and, in 1809 fifteen indigenous species were 

 known. In 1812 Colonel Montagu extended the number 

 to thirty -nine, and in 1852 Dr. Johnston further in- 

 creased the number to fifty-six. But from these we must 

 deduct eleven, which are only repetitions under new names, 

 or, otherwise, no species ; reducing the correct number of 

 species known to forty-five. 



In endeavouring to verify these species, I found, appa- 

 rently, insuperable difficulties arising from the exceedingly 

 unsatisfactory condition of the descriptive language em- 

 ployed by preceding authors, while, at the same time, I was 

 struck by the abundance of excellent characters that were 

 to be derived from the structural peculiarities of the ani- 

 mals. Up to the present time the Spongiadse h%ve been 

 classified either by their external form or in accordance 

 with their chemical constituents. In the second edition of 

 Lamarck's 'Anim. s. Vert.,' 138 species are included in 

 the genus Spongia, without the shghtest reference to their 

 internal structure ; and they are divided into seven groups 

 by external form only, the same characters serving also, iii 

 a great degree, to discriminate the species. 



Fleming, Grant, Johnston, and other modem naturalists, 

 ha,ve made their principal divisions depend on their che- 

 mical constituents, and have therefore constructed three 

 great divisions as genera -.—Spongia, composed of keratose 

 fibres unmixed, as it was supposed, with earthy matter ; 

 Halichondria, formed principally of siliceous spicula ; and 

 Grantia, having the skeleton composed of calcareous spicula. 

 Included in the second of these divisions are the genera 

 Tethea, Geodia, Pachgmatisma, Spongilla, Bgsidea, and 



