NATURAL HISTORY OF BHOMPSTON POND. 217 



worthy that the antennules and the antennae are unbranched, 

 differing in this respect from the Phyllopoda. Under certain 

 conditions it is possible to observe the small median eye (d) 

 shining with a brilliant light like some microscopic sparkling 

 gem. Respiration is performed over the whole surface of 

 the body, over which a continuous current of water is washed 

 by the setose branchial appendages. The eggs are attached 

 to water plants, and the larvae, possessing three appendages, 

 are laterally compressed, and enclosed in a thin bi-valve shell. 

 These tiny crustaceans can readily be examined in a watch- 

 glass, under a microscope, and their varied and wonderful 

 movements watched as they feed upon the animal debris of 

 the pond sediment. 



The third order of Entomostraca, namely, Copepoda, is 

 represented in this pond, particularly where the vegetation 

 is luxuriant and the water clear, by the common but no less 

 interesting and instructive form known as Cyclops (fig. 53). 

 On account of its median eye (a), which shines with a ruby 

 brilliance, this little crustacean was thus named after the 

 giant of Greek mythology. It has no carapace or shell, so 

 characteristic of the previous orders. The head is large and 

 round, but is not separated from the trunk ; it bears anten- 

 nules (b), antennae (c), mandibles, two pairs of maxillae, and 

 a pair of maxillipeds (d). The thorax bears four pairs of 

 biramous appendages, each consisting of a basal protopodite 

 (e), ending in a three-jointed setose exopodite (f) and an 

 endopodite (g). A copula (h) insures the simultaneous action 

 of each pair of these appendages, and assists the animal to 

 dart through the water in its characteristic manner. While 

 feeding it is sometimes noticed to glide more slowly and 

 smoothly through the water by movements of its antennae, 

 but, being more easily alarmed than the last animal, it is less 

 asy to observe its normal movements on the stage. The 

 first abdominal segment (i) bears a rudimentary fifth pair of 

 appendages, which are two-jointed in the female and three- 

 jointed in the male. The abdomen terminates in a caudal 

 fork (j). The adult females have a very characteristic 



