118 THE PELECYPODA. 



by " interfilamentary junctions," formed of 

 little opposing groups of cells whose cilia 

 interlock. In the higher Pelecypoda, this 

 form of junction gives place to horizontal bars 

 (like those of a gate), leaving water passages 

 of greater or lesser extent. The blood of the 

 mollusc passes down the interior of the 

 filament and thus is brought into close 

 proximity with the oxygenated water, which 

 is kept circulating over the Gills by means of 

 the ciliated epithelium which clothes the 

 filaments. P. J. R. 



