A Free-Living Copcpod. 95 



A FREE-LIVING COPEPOD 



(Cyclops sp.). 



SELECT a large female specimen (the females generally 

 have a pair of ovisacs suspended from the body) , and exam- 

 ine under a compound microscope. The body will be found 

 to be well rounded, neither depressed nor compressed, con- 

 siderably elongated, and clearly segmented. The divisions 

 into cephalothorax and abdomen are at once apparent. The 

 former consists of an anterior, unsegmented carapace, behind 

 which are four movable thoracic segments. Has the cara- 

 pace a rostrum ? Are the edges of the carapace free ? 

 Are the several thoracic rings all of about the same size ? 



In the present sex the abdomen has four segments, though 

 the first is in reality formed from two. Do you find any- 

 thing to suggest that fusion has actually occurred ? In the 

 smaller male there are five abdominal rings, the original 

 structure being retained. 



How many filaments are there arising from the terminal 

 abdominal styles ? Are there thoracic appendages ? Abdom- 

 inal appendages ? Note the position of the enlarged first 

 antennce. Are they provided with hair-like setce (olfactory 

 hairs) ? Compare them with the smaller second antennce. 

 In the males the antennae are reduced in size and functionize 

 as clasping organs. 



Examine the swimming appendages of the posterior por- 



