MOLL0SCA. 31 



in suspension millions of the spores (or seeds) of 

 Algse, ready to adhere and grow as soon as they find 

 a resting place, and these are particularly ahundant in 

 the warm season. Whether those of the green kindsj 

 the Ghlorosperrm, such as the JJlva, Enteromorpha, 

 and various kinds of Gonfervm, he more plentiful than 

 others, or whether they are more easily satisfied with 

 a place congenial to their growth, f know not ; but 

 these grow most obviously, in the proportion of a 

 thousand to one. Before we have kept our tank 

 stocked a fortnight, its transparent sides begin to be 

 sensibly dimmed, and a green scurf is seen covering 

 them from the bottom to the water's surface, which 

 constantly accumulates, soon concealing the contents 

 of the vessel from distinct observation. On examining 

 this substance with a lens, we find it composed of 

 myriads of tiny plants, mostly consisting of a single 

 row of cells of a light green hue, forming minute 

 threads which increase in length at the extremity ; 

 others display small irregularly puckered leaves of 

 deeper green, which develop themselves into Ulvm, 

 or EnteromorphcB. 



If we design the Aquarium to be of any service to 

 us in the observation of its contents, this growth must 

 be got rid of, or we might as well have a vessel with 

 opaque sides. Here then comes in the aid of the 

 Periwink. Exclusively a vegetable-eater, he delights 

 in the green sea-weed, and nothing can be more con- 

 genial to his palate than these tender succulent 

 growths. The little Yellow Winkle that I first spoke 

 of, possesses a similar appetite ; but he is less suitable 

 for the service required, inasmuch as his constitution 



