236 WILLIAM RAY ALLEN. 



been examined, and often contain little but the finest ingestible 

 material. This was well shown in the case of a Glccocapsa cul- 

 ture fed to a starved mussel. The culture was very pure except 

 for numerous fragments much coarser than the Glccocapsa itself. 

 There was an almost complete separation of Glccocapsa from the 

 other material by the gills themselves. Almost all the larger 

 fragments had been separated out by the gills themselves before 

 the finer had been agglutinated in mucus. Little of the former 

 was found in the masses present in the alimentary tract. 



The marsupial function of the gravid gill of the female inter- 

 feres somewhat with its respiratory and food collecting functions. 

 Ortmann ('12) has shown that secondary water tubes appear, in 

 which water circulates about the egg masses, and accomplishes 

 the aeration of the eggs and glochidia. Yet the volume of water 

 siphoned is much less than in the case of the non-marsupial gills. 

 This is well brought out by the fact that the gravid females almost 

 invariably regenerate the crystalline style much more slowly than 

 others. When kept under artificial conditions for some time the 

 gill-masses are usually aborted, another indication that the gravid 

 gills are unable to meet all the demand upon them. The greater 

 remoteness of the marsupial gill has suggested that it has become 

 differentiated for the storage of the eggs and has lost its food 

 collecting function. This notion is pretty well refuted by the 

 facts mentioned above concerning the regeneration of the style in 

 gravid females as compared with non-gravid females. It has 

 also been suggested that the mantle has taken over much of the 

 respiratory duty of the gills. If this were true the gravid female 

 should be under no special respiratory difficulty. When first 

 brought into captivity these females die at a much greater rate 

 tlfan others. The accessory water-tubes seem to be a very im- 

 perfect makeshift, sufficient perhaps for the glochidia, but afford- 

 ing the mother little aid. 



Since in the gills and palps there exists a mechanism well 

 adapted for the sorting of food ; since both observationally and 

 experimentally this mechanism is shown to accomplish a con- 

 centration of food ; and since the contents of the alimentary 

 canal have a decided green or brown color due to such concentra- 



