358 



THE FRESH-WATER MUSSEL 



or ostia (os), which lead from the mantle-cavity through a 

 more or less irregular series of cavities into the interior of 

 the water-tubes. The filaments themselves are supported 

 by chitinous rods, and covered with ciliated epithelium, the 

 large cilia of which produce a current running from the 

 exterior through the ostia into the water-tubes, and finally 



<(;/■ 



Fig. 95. — Diagram of the structure of the gill of Anodonta. 



The gill is made up of V-shaped gill-filaments (/) arranged in longi- 

 tudinal series and bound together by horizontal inter-filamentar junctions 

 (/. f. J) which cross them at right angles, forming a kind of basket-work 

 with apertures, the ostia (os), leading from the outside and opening {os') 

 into the cavity of the gill. The latter is divided by vertical partitions, 

 the inter-lamellar junctions (/. /. fj, into compartments or water-tubes 

 (w. t) which open also into the supra-branchial chamber ; b. v, blood- 

 vessels. 



(From Parker and Haswell's Zoology.) 



escaping by the wide dorsal apertures of the latter. The 

 whole organ is traversed by blood-vessels {b. v). 



The mode of attachment of the gills presents certain 

 features of importance. The outer lamella of the outer gill 

 is attached along its whole length to the mantle : the inner 



