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 



IV.t 



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 

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

 with apertures, the ostia (0s), leading from the outside and opening (of) 

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

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

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

 vessels. 



(From Parker and HaswelFs 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 



