588 
BULLETIN OF THE BUREAU OF FISHERIES 
going in and coming out of the ducts to the diverticula. Material on the ridged 
surface of the ducts always comes out and, at least from diverticula of the right side, 
follows the converging furrows to the mid-gut. 
In the stomach lies the gastric shield which doubtless takes the thrust of the 
rotating style, as described for other lammellibranchs. The shield (fig. 9,/ and g) 
is horny in consistency, ornately shaped, and of a somewhat greenish yellow color, 
with opalescence, which resembles rather strikingly the color of the lining of the mid- 
gut. Nelson (1918) believes the substance of the shield probably to be in the nature 
of chondrin, Gutheil (as noted by Yonge, 1926a) that it is secreted by the under- 
lying epithelial cells and Yonge (1926a) that it is formed of fused cilia. 
Extending into the stomach is the rodlike gelatinous crystalline style, clear green- 
ish amber in color and sometimes spirally marked. The shape, with the stomach 
contents removed from the “head,” is shown in the accompanying illustration. 
(Fig. 9e). Various workers (Barrois, 1889-90; Mitra, 1901; and Mackintosh, 1925), 
working with various genera have found the style to consist principally of water 
(about seven-eighths) and globulin (about one-eighth), and to contain digestive 
enzymes (Coupin, 1900; Mitra, 1901; and Dakin, 1909; Nelson, 1918; and Yonge, 
1926a). The style dissolves in water but is preserved by formalin, is quite firm in 
a freshly opened animal, and is concentrically laminated. The head, in the stomach, 
is found buried in a mass of food material which must be washed or teased away 
before the shape of this end can be determined. 
The markings to be found in or on some styles evidently are inclusions of food 
or some associated substance and presumably are spiral because of rotation of the 
style. Rotation of the style of lamellibranchs apparently was first observed by 
Nelson (1918) who opened the stomach for the purpose. More recently it has been 
observed through the shells of young mussels (Churchill and Lewis, 1924) and oysters 
(Yonge, 1926a), although I have not succeeded in observing it in Pecten. All obser- 
vations with which I am familiar are to the effect that, viewed from the head end, 
the style rotates clockwise. Nelson (1918 and 1925), Allen (1921), and Orton (1924) 
have supposed one of the functions of the style to be the return of food from gut to 
stomach. If the style markings are inclusions of material being so returned, the indi- 
cated direction of rotation is clockwise, if “streamers” from the stomach, it is counter- 
clockwise. From a consideration of the findings and opinions of recent workers it 
seems probable that they are the former and, therefore, that the rotation is clockwise. 
Moreover, in larvae identified as P. irradians I have observed the stomach contents to 
rotate rapidly in a direction corresponding with this clockwise rotation of the style. 
It is supposed that the style is not only continually revolved but also pushed into the 
stomach (against the gastric shield) where the head is continually dissolved. Fre- 
quently, in the stomachs of scallops possessed of a firm style, mingled with the rest 
of the stomach contents there is to be found a sticky, yellowish substance which 
apparently and presumably is dissolved material of the style. 
The nature and functions of the style have fascinated zoologists wito have evolved 
many theories. Of these the following may be worthy of mention: To act mechani- 
cally upon the food, apparently as a sort of chewing organ; to prevent the food 
passing too quickly through the alimentary canal before digestion can take place; 
reserve food material; an excretion; to lubricate the undigested food material; a 
digestive ferment. That the style contains an enzyme w T hich converts starch to 
sugar seems established, but just how important the enzyme of the style is in the econ- 
omy of digestion, has yet to be determined. Nelson (1918, 1925) believes that one 
