180 SELECTION AND TJSE 



The surface of the mud at the bottom of ponds of clear waier, 

 is frequently very rich in microscopic vegetable organisms. 

 These minute plants seem to seek the light, and to rise through 

 the mud which would otherwise cover them, so that by care- 

 fully scraping the surface of the bottom, we are enabled to 

 procure them in large numbers. 



It must, of course, be borne in mind, that while some species 

 are found in fresh water, others are marine, that is, they live 

 only in sea- water. The best locations for finding marine forms 

 are: 1, the pools of c'ear water, found in salt marshes; 2, 

 the surface of the mud at the bottoms of harbors and quiet 

 coves; 3, the waters of the ocean itself, as well as that of^the 

 bays and coves connected with it. 



The apparatus required for capturing these various objects, 

 is neither bulky nor expensive. For larvse and the larger ani- 

 malcules, the most useful implement is a small net. Ours con- 

 sists of a ring of brass wire (iron wire would rust and destroy 

 the net) about six inches in diameter, soldered to a tin tube or 

 ferrule, which fits tightly on the end of a walking cane. To 

 the ring is attached a bag of any light, gauzy material, which 

 possesses the two qualities of letting water out rapidly, and 

 keeping small objects in. With this net it is easy to capture 

 anything from a small fish or a frog to the very smallest larva, 

 and it is very portable, since an ordinary walking cane forms a 

 sort of universal handle for this and other implements. Next 

 to the net, we find the most useful articles to be bottles. They 

 should be of clear glass, so that any object contained in them 

 may be readily examined by means of a pocket lens. For this 

 reason we prefer what are called homoeopathic phials of large size 

 (half ounce and quarter ounce), and we generally carry a dozen 

 or two when out on a tramp. A fair sample of the contents of 

 a small pool is easily obtained by gently lowering the phial, 

 mouth downwards, under the water, and bringing it cautiously 

 to the place which is supposed to be richest in specimens. The 

 phial is then turned mouth upward, the air rushes out and the 

 objects are carried into the bottle by the force of the inrushing 

 current of water. For small, shallow pools, the phial is most 

 conveniently held in the hand, but when the water is deep a 

 handle is required, and for this we use the holder shown, in. 



