INTRODUCTIOX. 15 



species are more voracious than others^ and more danger- 

 ous. Thus, a friend of mine had a tank with a few small 

 fresh-water fish, and among them was a young pike, only 

 two inches long, which attacked, and in fact destroyed, other 

 fishes half as large again as himself. 



Rejjtiles. — Water Tortoises, and Newts, live well in tanks, 

 and are very interesting. They should be supplied with 

 mud at the bottom of their pond ; and also, by means of 

 floating boards or pieces of stone rising above tlie surface, 

 should have the opportunity of leaving the water at their dis- 

 cretion. Frogs do very nicely in Fresh- water Aquaria which 

 are surmounted by a fernery, wdiere they paddle in and out, 

 and dive in the water or hide among the ferns. 



MoUusca. — Beginning with the Tunicate order of Mol- 

 lusca, which are very simple in their composition, we find very 

 pleasing objects presented by several species of Ascidia, one of 

 which I have represented (Plate XIII.), probably A. hyaUna. 

 It is curious to see these apparently lifeless bottles with two 

 necks every now and then shut the openings and jerk out 

 the grosser particles of food, which they have admitted, in 

 the current. Those of the more compound nature are more 

 interesting to the microscopist than to the observer of out- 

 ward forms. Conchiferous MoUusca, or those furnished with 



