1 8 A NATURAL HISTORY OF THE SEAS 



cutting. A small portion is cut off, care being taken that 

 some of the outer skin is retained or the operation comes 

 to nothing, and under favourable conditions a cubic inch 

 of sponge will reach marketable size in about seven years. 

 Unknown to the bather myriads of embryo sponges 

 may surround him in the sea-water and many species 

 which from time to time appear in the Zoo Aquarium 

 brought in with fresh consignments of Atlantic sea-water 

 are unsuspected until they attain to discernible proportions. 



