THE OSTRACODA 803 



Notodromas appears purely as a summer form. It winters in 

 different "egg stages," develops in April or May, and by Septem- 

 ber has entirely disappeared. Cypridopsis vidua and Cypris in- 

 congruens appear in early spring and last until late autumn. The 

 spring forms appear to have a much shorter life history. 



These forms may be collected in great variety and abundance 

 by drawing a Birge or cone net through submerged plants present 

 in ponds, slow streams, and lakes, and by stirring up the bottom 

 ooze and slime, and drawing the weighted net to and fro over the 

 bottom. 



In this manner not only the free-swimming forms may be cap- 

 tured, such as Cypris, Cypridopsis, etc., but typically bottom forms 

 such as Candona, Herpetocypris, etc., may also be included. By 

 emptying the mud and all other accumulations in a beaker of 

 water, and stirring well, it will usually result in many of the Ostra- 

 coda getting air caught between their valves, thus causing them to 

 float on the surface, from which they may be readily removed 

 with a "medicine dropper" or pipette. The use of a small hand 

 lens is advisable in determining whether or not Ostracoda are 

 surely present. In any case, the "catch" may now be concen- 

 trated by carefully pouring off the contents of the beaker from 

 the sediment in" the bottom into a small dip net made of Swiss or 

 bolting cloth. 



After washing out as much of the soluble or other matter as is 

 possible, the remainder may be emptied into a Syracuse watch 

 glass or other shallow vessel containing but a small quantity of 

 water. Thus the catch is condensed to such bulk as may now be 

 easily transferred to small vials of preservative fluid such as 90 

 per cent alcohol, or a mixture of 80 per cent alcohol and glycerin 

 in about the proportion of 10 to i. However, killing had better 

 be done in about 70 per cent alcohol, which should be gradually 

 increased in strength, as in this manner the shells are more 

 likely to remain open than when killed in alcohol of a higher 

 percentage, 



If a large quantity of living forms should be desired, the entire 

 catch of a locality may be poured into a special pint strainer jar 

 (Fig. 1248). 



