154 OTHER CRUSTACEANS 



and the zygotes become attached to the hairs of the abdominal ap- 

 pendages of the female. The pre-hatching, or embryonic stages, and 

 also the post-embryonic, or larval and juvenile stages, can be observed 

 if egg-bearing females are available. Examine in a watch glass of 

 water the attached stages and juveniles about ready to leave the 

 parent (c/. Fig. 68). 



OTHER CRUSTACEANS 



Exercise 1. — The Smaller Crustacea, or Entomostraca. 



(a) The older division of the Class Crustacea into the subclasses 

 Entomostraca and Malacostraca is still useful for the separation of 

 certain smaller and simpler crustaceans from the larger and more 

 familiar forms. Water-fleas and copepods are representative Ento- 

 mostraca. 



(b) The name water-flea was given by the early microscopists to 

 the minute crustaceans of which the Genus Daphnia is an example. 

 These are common in fresh water. They may be watched as they 

 swim in an aquarium and studied in a watch glass with handlens and 

 compound microscope. Addition of ether or chloretone produces a 

 temporary anesthesia which facilitates the study. 



(c) The body, consisting of head, thorax, and abdomen, and the 

 appendages are covered laterally with a carapace, as if the carapace 

 of the crayfish were extended ventrally and posteriorly so that the 

 abdomen and appendages became enclosed. The organs of locomotion 

 are enlarged antennae. Do you find antennules? Look for the single 

 eye, the heart, which should be still beating, the digestive tract, and 

 any other features, recalling what has been seen in the crayfish. Under 

 the dorsal portion of the carapace in the female is a brood-pouch, in 

 which eggs and embryos may be found. The young are liberated as 

 miniature adults. Make a drawing, 6-8 cm. in length, of the animal 

 from a lateral view. 



(d) The forms called copepods are another type of these small 

 crustaceans, of which the Genus Cyclops is a fresh-water representa- 

 tive. Watch copepods swimming about in an aquarium ; then study an 

 anesthetized specimen on a slide and held lightly with a cover glass. 

 The thorax with its carapace is shaped like a pear cut in half. The 

 abdomen projects posteriorly and is tipped with hairlike processes. 

 The single eye suggests the fabled "cyclops." As in Daphnia, the 

 antennae are the organs of locomotion. How are the remaining ap- 

 pendages distributed? Females may show an egg-sac projecting on 

 each side of the abdomen. The young hatch as larvae with three pairs 



