Ostracods 187 



progeny of a single female might reach the astounding 

 number of 13,000,000,000 in sixty days. 



The Ostracods are minute crustaceans, averaging 

 perhaps a millimeter in length, having the head, body 

 and appendages all inclosed in a bivalve shell. The shell 

 is heavier and less transparent than that of the water 

 fleas. It is often sculptured, or marked in broad patterns 



Fig. 93. One of our largest water-fleas, Eurycerus lamellatus, 



twenty times natural size. Note the eggs in the brood chamber 

 on the back. Note also the short beak and the broad post- 

 abdomen (shaped somewhat like a butcher's cleaver) by which 

 this water-flea is readily recognized. 



with darker and lighter colors. The inclosed appenda- 

 ges are few and short, hardly more than their tips show- 

 ing when in active locomotion. There are never more 

 than two pairs of thoracic legs. The identification of 

 ostracods is difficult, since, excepting in the case of 

 strongly marked forms, a dissection of the animal fr >rr 

 its shell is first required, 



