9O THURLOW C. NELSON. 



Schrader on the food of mussels. This investigator found that 

 only about one half of the diatoms and green algae taken in were 

 digested, and he concluded that these organisms play a com- 

 paratively unimportant role in the food supply of mussels. He 

 apparently was unaware that in the process of sorting over of the 

 acquired food materials by the ciliary tracts of the stomach, aided 

 by the rotation of the crystalline style, many food organisms are 

 shunted off into the intestine along with the sand and dirt. 

 Especially may this be true of relatively heavy forms such as the 

 diatoms. Some of these escaped food organisms may be passed 

 across the typhlosole into the style sac and thus eventually be 

 returned to the stomach, but a considerable number escape 

 undigested from the anus. Blegvad '15 likewise draws false 

 deductions as to the "insignificant" role played by plankton 

 organisms in nutrition, from the finding of living planktonts in the 

 faeces of the European oyster. 



While at Madison, Wisconsin, I kept Anodonta and Lampsilis 

 for months at a time in clear running water in which the chief food 

 supply consisted of desmids, diatoms, and nannoplankton forms 

 most of which were growing upon the sides of the tank and upon 

 the shells of the mussels themselves (Allen, '14). Examination 

 of the intestinal contents revealed many living organisms but also 

 the empty tests of numerous diatoms which had been digested. 

 Imperfect as may be the mode of separation of food from dirt by 

 the ciliary mechanisms within the alimentary canal of bivalves, 

 the wonder is that it functions as efficiently as it does. Such 

 living organisms as are cast out in the faeces are not altogether 

 lost since they accumulate on the shells or upon nearby objects, 

 where they multiply rapidly within the faecal remains and form a 

 rich growth which is continually contributing its quota of food to 

 the siphons of the mollusc (Allen, '14; Martin, '23). 



Allen ('21) gives a detailed account of experiments on the 

 effects of various food organisms in the formation of the crystal- 

 line style of fresh-water mussels. The details of this work cannot 

 be discussed here, but in general they confirm and extend the 

 findings of his preliminary paper (Allen, '14) and my own con- 

 clusions (Nelson, '18) regarding the role of food in style regener- 

 ation. He further showed that nannoplankton is relatively more 

 effective than is net plankton in effecting style formation. 



