CRYSTALLINE STYLE OF LAMELLIBRANCHS 105 



which a certain amount of selection and separation of the ma- 

 terial in the stomach does take place. 



In artificial feeding experiments I have found that the selec- 

 tive action of the palps of Ostrea is very great as compared with 

 that of Modiolus, even the most finely divided carmine grains 

 being rejected. Coincident with the increase of selective power 

 on the surface of the body there is a corresponding lack of 

 specialization of the wall of the stomach for sorting over the 

 alimentary matter. 



Summing up what has been said of the origin of the style in the 

 developing embryo (p. 88), together with the above description 

 of the process of feeding in the adult Modiolus, it is evident that 

 one of the primary and important functions of the crystalline 

 style throughout the life of the lamellibranch is to aid in keep- 

 ing the alimentary mass in the stomach in motion.^ This move- 

 ment is necessary, not only as a means of sorting out foreign 

 matter in the stomach, but also as a substitute for muscular 

 peristalsis in keeping the food in motion. 



Since the head of the style with sand grains and other rough 

 objects attached to it bears against the stomach wall, there is 

 necessarily developed at this point a resistant structure to pre- 

 vent injury to the epithelium. The gastric shield therefore 

 arose as such an organ of protection, as was first believed by 

 Barrois, who compared it to the 'Trichter' of insects and some 

 other arthropods. 



Barrois, followed by Pelseneer ('91) and others, believed that 

 the function of the style, when dissolved, consisted in surround- 

 ing sharp particles and thus preventing injury to the epithelium. 

 Against this interpretation I would urge the following objections: 

 First, the style, allowed to dissolve of itself without the addi- 

 tion of any fluid, forms, with the exception of the inner core, 

 a liquid of such a thin consistency as to be of little or no pos- 

 sible value as a protective covering; second, the cells of the 

 alimentary tract are covered with a heavy carpet of large cilia, 

 so that no sharp object would be likely to come in contact with 



* Milne-Edwards ('59) was the first to advance this theorj-, but without the 

 least evidence in its support. 



