428 TJie Strticture and Life-History of a sponge. [Sess. 



tlie upper teeth, from some cause or another, after having 

 grown so far into the mouth, turned outwards again, and then 

 backwards, until at last they formed a complete circle. We 

 arrange with the keeper for the head, and take it with us for 

 exhibition to the members of the Edinburgh Field Naturalists' 

 and Microscopical Society; and now produce it to convince 

 them that there is a substratum of fact in our short imagina- 

 tive expedition into the country. 



Yll.—THE STRUCTURE AND LIFE-HISTORY 

 OF A SPONGE. 



By Mr JOHN LINDSAY. 



{Read Feb. 25, ISOl.) 



The various species of sponges throughout the globe that have 

 been classified and described up to the present time are very 

 numerous. The Challenger Expedition alone has added a 

 large number hitherto unknown to science, and many more, 

 no doubt, will yet be discovered. Even the nxxmber of 

 British marine and fresh-water forms now known is consider- 

 able. As evidencing the advance which has been made in 

 our knowledge of this single group of animals during the last 

 half century, it may be mentioned that while Dr George 

 Johnston, in his ' History of British Sponges and Lithophytes,' 

 only enumerates some sixty species, the fourth or supple- 

 mentary volume of Bowerbank's 'Monograph of the British 

 Spongiadfe,' published by the Eay Society in 1882, — after the 

 author's lamented death, — under the editorship of the Ptev. 

 A. M. Norman, contains a list of no fewer than 284 species. 

 While such advances have been made at home during that 

 period, there have been corresponding additions to the number 

 of foreign species. Amongst so many forms, — ranging from 

 our native burrowing-sponge (Cliona cclaia), a mere dot of a 

 creature, which bores its way into oyster and other shells, to 

 the large tropical species known as Neptune's drinking-cup 



