224 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



second maxillss and not the maxillipeds to which the filament is 

 transferred. The tips of these second maxillae do not unite to form 

 the button, they are simply stuck to the proximal end of the filament 

 (fig. 44). Although the claws subsequently disappear and the 

 maxillae apparently fuse, sections show that each really preserves its 

 identity; that is, the fusion is only apparent and not real. 



10. In the second copepodid stage sex distinction is possible. 

 The body of the male is strongly constricted into a waist between the 

 head and thorax; the second maxillae are stout and no longer than 

 the maxillipeds. The body of the female is long and slender and 

 only slightly constricted; the second maxillae are much longer than 

 the maxillipeds and slender. 



11. In this second copepodid stage the digestive tract of the male 

 is not yet opened at the anus, but it is completed in the female. The 

 sexual organs have begun to develop and the large maxillary and 

 maxillipedal glands are forming. The nervous system is concen- 

 trated in the infra-oesophageal ganglion, and there are no ganglia 

 on the ventral nerve cord. 



12. This second copepodid larva molts into the adult form. 

 We have here then a marked concentration of development, the 

 nauplius and metanauplius stages passed inside the egg and so 

 fused as to be indistinguishable, the first copepodid the only free- 

 swimming stage, and of very short duration (twenty-four to forty- 

 eight hours), just long enough to find a host, the second copepodid 

 stage showing the beginning of all the organs and molting directly 



into the adult. 



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