38 THE VIVARIUM. 
(Menyanthes trifoliata), which should be a small plant ; the Brook- 
lime (Veronica beccabunga, Fig. 28) ; the Water-mint (Menthasylves- 
tris); Watercress (Nasturtium officiale); the Greater Duck-weed 
(Lemna polyrhiza, Fig. 29); the Thick Duck-weed (Lemna gibba, 
Fig. 30) ; the Lesser Duck-weed (Zemna minor, Fig. 31) ; the Ivy- 
leaved Duck-weed (Lemna trisulca, Fig. 32). Except the first 
Fic. 26.—VERNAL WATER STARWORT (Callitriche verna). 
two of the above plants and the Duck-weeds, all may be planted 
anywhere in the Vivarium. 
This case is very suitable for such Batrachians as Frogs, Toads, 
Newts, Axolotls, and the like. A tank 3ft. long, 2ft. wide, 16in. 
deep, is a very good size for such a purpose as this. Water- 
Tortoises might be kept in this Vivarium, but they will fre- 
quently disarrange the gravel not a little. At the pond end of 
