MOLLUSCA 75 



podectathentous. These are the Eotifera, which do not form 

 a secondary body cavity ; the Bryozoa (Polyzoa), or sea mats, 

 which only offer hints of such a cavity ; the Brachiopoda, or 

 lamp shells, in which a secondary cavity is well developed, 

 as it is in the Phoronidea and in the Sipunculoidea. The 

 Kotifers possess only protonephridia. In the coelomate forms 

 the protonephridia establish a connexion with the coelom and 

 function as kidneys and gonoducts. 



In primitive Mollusca there is an association of pericardial 

 cavity and gonad, and the sex cells of the latter are expelled 

 by the coelomiducts, which are thus kidneys and gonoducts. 

 In the Pelecypoda, as in the higher Mollusca generally, the 

 gonads are separated from the pericardial cavity and acquire 

 separate openings to the exterior, but the tubular gonads are 

 nevertheless coelomic in origin. 



