CRYSTALLINE STYLE OF LAMELLIBRANCHS 101 



stomach. Though surmised by several former workers from the 

 co-axial layers of which the style is composed, I am unable to 

 find any statement in the literature indicating that this rotation 

 has actually been observed. 



After nearly two years of experimenting, in which many indi- 

 viduals, both marine and fresh-water, were opened, I was able 

 finally to cut through the stomach wall and expose the head of 

 the style in such a way that the animal did not contract unduly, 

 with consequent displacement of the alimentary canal.* 



As a result the style is not put under tension, but is free to 

 rotate in the style sac, in spite of the fact that it forms a U-shaped 

 bend in following the course of the intestine. To my surprise, 

 I found this rotation to be quite rapid. In Anodonta kept at 

 a constant temperature of 11.5°C. prior to, and during the ex- 

 periment, the maximum number of revolutions per minute was 

 eleven. In Modiolus, at 25°C., the maximum number per 

 minute was thirteen. The direction of rotation in both species 

 is clockwise when viewing the animal from the anterior end. 

 (Compare this with the direction of rotation of the food particles 

 in the stomach of the veliger larvae of Ostrea and Venus, p. 88.) 



The food material in the stomach, entangled in mucus, be- 

 comes wound about the head of the style, and whirled around in 

 the lumen just posterior to the gastric shield. So strong is the 

 tractive force of the rotating style that strings of mucus from, any 

 part of the body, if led to the stomach cavity, are at once drawn 

 in and wound up in the food mass. 



While rotating the style in this manner, the cilia of the style 

 sac push it anteriorly against the gastric shield, with force 

 enough to cause the style to bow out when the stomach walls 

 are drawn apart. In Modiolus, at 25°C., this forward move- 



* The technique employed is as follows: An individual which has been siphon- 

 ing vigorously is removed from the water, and the right valve removed by pass- 

 ing a sharp, thin scalpel between the shell and the adductor muscles, leaving 

 the latter intact. The mantle and gills are then laid back, and a small incision 

 is made in the body wall over the dorsolateral region of the stomach. At this 

 point the stomach wall comes very close to the surface in those species I have 

 studied. By means of fine hooks, the cut edges of the stomach are pulled apart 

 to expose the head of the style where it bears against the gastric shield. 



