96 THURLOW C. NELSON. 



habits and the habitat of the molluscs. This aspect of the 

 problem is discussed likewise by Robson ('22) for the style sac and 

 intestine of gastropods as well as of lamellibranchs. 



Criticisms of Vonge's work are, first, his failure to consider the 

 important role of the leucocytes in digestion, especially of fat; 1 

 and second, an inadequate appreciation of the part played by the 

 hepatopancreas in the digestion and absorption of food as 

 demonstrated by List ('02). From microscopic examinations of 

 this organ during the later stages of digestion in Ostrea and 

 especially in Modiolus I am led to believe that in these forms even 

 more food is digested in the hepatopancreas than in the stomach. 

 I believe the functions of the stomach, in some lamellibranchs at 

 least, to be chiefly those of sorting over of food materials and the 

 final separation of dirt, and of mixing food and enzymes, rather 

 than those of an organ where complete digestion is effected. 



Lazier ('24) in a valuable paper on the morphology of the 

 digestive tract of Teredo navalis confirms for Teredo the con- 

 clusions of my 1918 paper regarding the origin and function of the 

 crystalline style. His investigation of the morphology of the 

 stomach, style-sac, and intestine shows that these structures are 

 essentially similar to those of other molluscs in which the style- 

 sac is completely separated from the intestine. The style of 

 Teredo is believed to be rotated in the manner I described for 

 Modiolus, and in Anodonta, although the actual rotation was no 

 observed by Lazier. 



In some of the marine borers, however, (Pholas and Martesiaj. 

 for example) the style is of such proportions that if rotation occurs 

 it must be very slow. In my 1918 paper is figured a transverse 

 section of Martesia showing a style of a mass approximately 

 equivalent to the entire remainder of the body exclusive of the 

 gills. This aspect of the problem needs further investigation, 

 especially as to the part played by the style in the acquisition and 

 possible sorting over of the borings ingested by Teredo and its 

 wood-boring allies. 



Churchill and Lewis ('24) make a valuable contribution to our 

 knowledge of the mechanism of feeding in young bivalves. No 



1 A recent paper by Vonk '24 gives a good summary of the work in this field and 

 adds some original observations. 



