PCECILOPODA. 



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Cyclopoidea are properly a pair of legs. The mouth has thus one pair 

 less of appendages, including only a pair of mandibles and a pair 

 of maxilla?; even the maxillse are sometimes obsolete, and where 

 present are often true maxillipeds. 



I. PCECILOPODA. 



The Poecilopoda are intimately related to the Cyclopoidea. They 

 diverge more and more widely from that group as the species descend 

 in rank, and the lowest of them bear but a faint trace of the typical 

 form or structure. 



In one section, that most closely Cyclopoid, the eight natatory legs 

 have the ordinary form, and the body is usually subcylindrical or 

 subterete, without a proper carapax ; moreover, the female carries the 

 embryos externally in sacs or bags, as in Cyclops or Corycseus. These 

 are the Ergasiloidea. 



In a second section, the eight natatory legs are equally present, 

 though often changed in part to apron-like appendages, the body is 

 depressed and has commonly a large peltate carapax, and the female 

 carries the embryos externally in two long tubes, containing the ova 

 in a single series, — a mode of structure not found in the Cyclopoidea. 

 Rarely, as in Argulus, there are no external tubes, the ova becoming 

 free directly from the oviduct ; but the structure of such species is 

 still essentially the same, as in the Caligi. These are the Caligoidea. 



The variations in form among the natatory legs in the Caligoidea 

 are very great, and these modifications, as we pass to lower forms, 

 end in the obsolescence of these legs; and while the posterior part of 

 the body "thus loses its members, the anterior part often fails in the 

 first pair of antennas. Such are the Lernjsoidea. The body may be 

 thick and short, or long and worm-like. The appendages are at times 

 all obsolete, excepting one or two short jointless processes attached 

 to the head or anterior part of the body. The eggs in the Lernseoidea 

 are carried externally, sometimes in bags or sacs, as in the Ergasi- 

 loidea, and sometimes in slender tubes, as in the Caligoidea. 



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