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species in the United States. Of course the children will demand names 

 for the numerous things which they may chance to see, but few Botan- 

 ists or Zoologists could give them all. A frequent examination of pond 

 scum from different sources will allow the children to become familiar 

 with some of the most common torms which will repeatedly occur. The 

 names of many of these may be ascertained and supplied in time. 



DIATOMS. 



Diatoms are almost always present in the above described prepara- 

 tions. They are small objects, generally brownish in color, often taper- 

 ing at each end like a canoe. They move across the field like small 

 boats. There are many other shapes than these among the diatoms. 

 These are plants having delicate shells of silica. When the plant dies, 

 the shell drops to the bottom of the pond. In certain positions, ponds 

 or lakes, which have been the homes of diatoms for ages, have a deposit 

 of fine mud at the bottom made up largely of diatom shells. In ancient 

 geological times there were thus formed in some places in California 

 and in other countries, deposits making thick strata of rock composed 

 almost wholly of diatom shells. 



If in the first lesson neither spirogyra nor diatoms are in the material 

 observed, equally interesting forms will be seen, some of which will be 

 described later. 



riosquito Eggs. 



The eggs of the mosquito are laid on the surface of the water of ponds, 

 ditches and the like. They may often be found floating in watering- 

 troughs. They form a small, black mass, which, when not closely 

 examined, might be taken for specks of soot. These little floats consist 

 of long, slender eggs adhering closely. Each egg is made up of a case 

 pointed above and opening by a cap below, the egg proper being within. 

 As the larva of the mosquito hatches out, the cap drops down and the 

 larva, the "wriggler" or the "wiggle-tail," as the children know it, 

 comes out and swims away. 



If a few floats of eggs can be obtained some can be used for examin- 

 ing the eggs with the lower power of the microscope; the remainder 

 may be placed in a small vessel of water, and the tranformation ob- 

 served. The larvae when first hatched are very small and almost trans- 

 parent. At this time they make most interesting objects under the mi- 

 croscope. The beating of the long vessel, which serves as a heart, may 

 be seen; also the internal tubes (trachge) which allow the air to pene- 

 trate the body. These are connected with the breathing tube, which is 

 a sort of spur from the posterior end of the body of the larva. When 

 at rest and not disturbed, the "wriggler" comes near the top of the 

 water, and extends its breathing tube to the surface, allowing its head 

 to hang down, At the end of the tube are a number of plates which 



