CHAPTER VII. 



MOLLUSCA, CRUSTACEA AND REPTILIA FOR THE FRESH-WATER 

 AQUARIUM. 



Use of Mollusca— Greatest Variety of Mollusca to be looked for in the Ocean — 

 Univalves and Bivalves— Lymnea columella— Lymnea fragilis— I'hysa hctcrostro- 

 pha— " Walking on the Air,"— Eggs of Physa— Production of Young— Right-hand- 

 ed and left-handed Shells— Physa plicata— Planorbis bicarinatus— P. lentus— 

 P. armigerus— P. corpulentus— P. exacntus— P. parvus— Paludina decisa— Mela- 

 nia— Unio complanatus— U. radiatus— Anodon fluviatilis— Craw-flsh— Fresh-water 

 Shrimps— Asellus communis— Branchipus stagnalis— Cyclops quadricornls— Bull- 

 frog— Croak of the Frog— Transformations of the Frog— Spring Frog— Marsh Frog- 

 Water Lizard— Red Salamander. 



It will be remembered how, when speaking of the prin- 

 ciples of the Aquarium, it was said that a green scum 

 would, after a time, form on the glass sides and so ob- 

 scure our view of the interior ; now, for the purpose of 

 removing this so that a clear and unobstructed sight of the 

 habits and actions of our pets can be procured, we follow 

 the experienced example given us by Mr. Warrington, and 

 place in our Aquarium Nature's scavengers, the little fresh- 

 water snails. In a fresh-water tank the Mollusca are 

 represented only by these pretty little creatures, for 

 though many writers on the subject have asserted that 

 they are necessary evils, the sight of which is only to be 

 borne because of their usefulness in rendering and keeping 



