398 



IWVmiTEBRATE MORPHOLOGY. 



formed by the fusion of the upper and lower lips. The 

 second maxillae (mx) develop at their bases large suckers, 

 while the first thoracic appendages, here termed maxilli- 

 peds, are limblike and have also hooked processes upon the 

 basal joints. These are succeeded by four pairs of biramous 

 swimming appendages. 



A well-developed heart is present, giving rise to arteries 

 extending throughout the length of the body. A pair of 

 lateral compound eyes (pc) are also present, and a further 

 difference from the majority of the Eucopepoda lies in the 

 fact that the eggs are not carried by the female, but are de- 

 posited on foreign bodies. 



All the forms are parasitic, in some cases, as ArguLus, 

 upon fresh-water fishes, but they also possess the power of 

 swimming actively. 



4. Order Cirrhipedia. 



The Cirrhipedia or Barnacles are without exception ma- 

 rine forms, and in the adult condition either adhere to foreign 



P, 



Pig. 180. — Cypris Larva of Zepas (after Claus). 

 Ab = iibdomeu. Oc = eye. 



AP = antennules. Ov = ovary. 



Cg = duct of cement-gland. p = penis. 



o = opening of oviduct. T^ = third tliorncic foot. 



bodies, leading a perfectly sessile life, or olse bore in the shells 

 of certain Mollusca, or finally are parasitic. It will be con- 

 venient to describe first of all the organization of the sessile 

 and boring forms, later considering briefly the parasitic forms 

 which show many peculiarities due to degeneration. 



During the course of development the Cirrhipedia all pass 

 through a larval stage similar in general appearance to an 



