118 NATURE STUDY 



which are so abundant at ten cents each, and so seldom 

 worth buying. The latter are very apt to be consump- 

 tive, and, indeed, are frequently sold w'hen in the last 

 stages of consumption. A dorsal hump back of the head, 

 ventral flatness, and rather frayed-out fins are sure indi- 

 cations of the disease. 



The fish should not be too large nor too numerous. If 

 you are so fortunate as to have a good northern exposure, 

 and if the room is not overheated, a dozen medium-sized 

 fish will not be too many in a five-gallon aquarium. 



Young minnows, dace, black-banded sunfish, may he 

 safely placed with gold fish, as well as tadpoles, snails, 

 and mussels. Eels, sunnies, catfish, mud minnows, cray- 

 fish, beetles, must be cared for separately. 



It is better to keep a few gold fish first, experimenting 

 later with the less hardy but more interesting kinds. 

 Snails, tadpoles, and mussels, however, do not complicate 

 the feeding, and do add variety. 



There are two kinds of pond snails, — those which 

 breathe by means of lungs, Limnea -(large), Physa 

 (small), and those which breathe by gills, Paludina (large). 

 The large species cost sometimes five cents each, while 

 for the same sum a dozen of the smaller ones may be 

 purchased. For teaching purposes, Limnea is particu- 

 larly valuable, but it cuts up the plants. 



Mussels and tadpoles are cheap. Tadpoles bought 

 now are not likely to develop much more until spring. 

 Feeding them on raw^-scraped beef, and keeping them in 

 a warm room, often hastens the process. 



Feed every other day. A piece of the prepared fish 

 food two inches square ought to be sufficient for a dozen 

 medium-sized gold fish. Snails, mussels, and tadpoles do 

 not require special feeding. It is a good plan to give all 



