72 COMPARATIVE ANATOMY AND PHYSIOLOGY 



Lsemodipoda are modified by parasitism, and have 

 the abdominal region rudimentary (e.g. Cyamus, which 

 is found on the skin of whales). 



Fig. 32. Ammothoa pycnogonoides. 



B. The Araclmida are arthropods, in which the 

 mouth is never placed so far back that any of the 

 appendages become antennary organs ; the second and 

 succeeding four (at most) pairs of appendages have 

 their basal portions ranged round the mouth, the 

 functions of which these parts subserve. The free 

 portions of the six anterior appendages take on various 



