A COPEPOD 53 



CRUSTACEA 



A FREE-SWIMMING COPEPOD {Cyclops) 



These minute animals are representatives of the division of 

 Crustacea called the Entomostraca. All of the crustaceans 

 heretofore studied belong to the higher group called Malacos- 

 traca. Copepods are extremely common in both fresh and salt 

 water. They may be obtained in almost any permanent pool 

 of water in the woods or fields or from the surface water of the 

 sea, often in large quantities, and are easily kept in aquaria. 

 The animals should be studied alive if possible. Place several 

 on a slide under a cover-glass and examine them under a micro- 

 scope. If the pressure of the cover-glass does not suffice to 

 keep them quiet, the withdrawal of some of the water from 

 under the cover-glass with blotting-paper will probably accom- 

 plish this result. Also stain and mount a number of copepods 

 in balsam or glycerine. Observe the cylindrical body and the 

 two pairs of long antennae with their sense-hairs ; also the long 

 spines at the end of the abdomen. Note the division of the 

 body into abdomen and cephalothorax, and also that the latter is 

 not covered by a carapace. If the animal be a female it may be 

 carrying a pair of egg-sacs filled with eggs extending from the 

 anterior end of the abdomen. Note the median eye, also the 

 intestine and muscle fibers, through the transparent body-wall. 



The body is made up of fifteen somites, the head, thorax, and 

 abdomen each containing five. The head is relatively large, and 

 its somites are fused together ; they bear the cephalic append- 

 ages common to all crustaceans. The first pair of antennae is 

 longer than the second ; in the male it is secondarily modified 



