S( 



CRUSTACEA COPEPODA 



the mouth and its appendages, dividing the free-living and 

 semi-parasitic forms as Gnathostoniata from the true parasites or 



Fig. 25. — Calanus Ayperborens, x 30. Abd^, First abdominal segment ; 1st Ant, 

 Bnd Ant, 1st and 2nd antennae ; Md, mandible ; Mx^, Mx', 1st and 2nd maxillae ; 

 jl/a;_p, maxillipede ; Th'^, 1st thoracic appendage. (After Giesbreclit.) 



Siphonostomata. This division, although convenient, breaks 

 down in many places, and it is clear that the parasitic mode of 

 life has been acquired more than once in the history of Copepod 



