8 



U. S. BUREAU OF FISHERIES. 



live amonp- water plants or in the ooze on the bottom. The,y may 

 frequently be observed as swarming specks in pools whei-e algee and 

 decaying plants abound. 



The reproductive process and. therefore, the abundance of ostra- 

 cods seem to be affected to a notable degree by the environment. The 

 amount of light, the variations in temperature, the nature of the 

 bottom, the presence or absence of algse, the composition and rate of 

 flow of water, all have their effects in one way or another. Direct or 

 intense light accelerates all their life processes. Shady or dark areas 

 in pools are not likely to contain certain free-swimming forms, while 



Avell-lighted places may contain them in 

 abundance. Uniform distribution of 

 light is conducive to a uniform distribu- 

 tion of these forms. On the other hand, 

 the more stationary forms are more likely 

 to occur in the deeper and darker places, 

 in the ooze and slime of the bottom. How- 

 ever, some forms seem indifferent to 

 whether it is light or dark, shallow or 

 deep water. Unpolluted water appears 

 to be essential to the well-being of the ma- 

 jority of forms, although practically no 

 forms occur in spring water and running 

 water is not especially favorable. Some 

 forms are very tolerant of extreme stag- 

 nation and some seem even to favor stag- 

 nant water. 



Most ostracods subsist upon either ani- 

 mal or vegetable food, and small animals 

 form a considerable portion of their diet. 

 Some will eat their own kind if the opportunity offers. Some species 

 have been observed skeletonizing leaves. It is stated that in captivity 

 most forms will eat from thin slices of potato. Their great numbers 

 and greediness oftentimes make them very efficient scavengers and 

 effective agents in purifying standing water. 



Most species of ostracods are bisexual, but a few are represented by 

 females only, which reproduce by unfertilized eggs. Their eggs are 

 said to have a remarkable vitality as do those of phyllopods and some 

 Cladocera. An ins-tance is on record of samples of mud being sent 

 to England from Jerusalem and Entomostraca (Cypris and Daph- 

 nia) being raised from them after a lapse of from 24 to 30 years. 

 G. O. Sars, of Norway, has reported raising them from dried mud 

 sent him from Australia and China. Some species of ostracods may 

 be found throughout the year in different degrees of development 

 under the ice in winter. Mud collected from the bottom in winter 

 and placed in water in a moderately warm place may very soon 

 yield plenty of one or more species. Some forms occur only as sum- 

 mer forms, or from early spring to late autumn. The duration of 

 life of the spring forms appears to be much shorter than that of 

 the others. 



The numerous species of ostracods vary in adult length from at 

 least as low as 0.42 to as high as 8.60 mm. "(about 0.016 to 0.14 inch). 

 The most common North American ostracod is Cypridopsis vidua. 



Fig. 4. — Ostracod. Two varie- 

 ties. Cypris fuscata. a and b, 

 dorsal views ; c, side view of a. 

 Enlarged 20 times. After 

 Ward and Whipple. 



