The connective tissue around the sac and under 

 the typhlosoles consists of typical vesicular cells. 



In actively feeding oysters the lumen of the sac 

 is occupied by a gelatinous rod with a bulging head 

 protruding inside the stomach (fig. 203) and the 

 pointed tail extending to the distal part of the sac. 

 The color of the style varies from greyish white 

 to deep yellow and brown, depending on the type 

 of food consumed by the oyster. The head is 

 usually darker than the rest of the style because 

 of the food particles ^v^apped around it. 



Inside the sac the style is rotated by the ciliary 

 action of the epithelium. The rotary motion 

 was originally suggested by List (1902) in his 

 work on mussels, but the demonstration that the 

 rotation actually takes place in Anodonta and 

 Modiolus was made by Nelson (1918). According 

 to Yonge (1926a), the large cilia of the groove of 

 the sac of 0. edulis move in such a way as to 

 produce a slow clockwise rotation of the style 

 when seen from the stomach. There is, however, 

 a tract of cilia on the side of the larger typholsole 

 which beats in the direction of the stomach and 

 presumably pushes the style forward. Food 

 particles that enter the sac are carried by the 

 currents down the gut but some of them tangle 

 in the substance of the style, are wrapped around 

 it, and carried back to the stomach. This process, 

 observed by Nelson (1918, 1925), Allen (1921), 

 and Orton (1924), may be significant for the bi- 

 valves in which, like in Ostrea, the style sac is in 

 direct communication with the midgut. 



As the style rotates and rubs against the gastric 

 shield, aiding in mixing and grinding food particles 

 it slowly dissolves in the gastric juice and yields 

 digestive enzymes. 



FORMATION 



The crystalline style is not a permanent struc- 

 ture. In oysters removed from water and left in 

 the ah- the style dissolves in a short time. This 

 observation, reported for 0. edulis by Orton (1924), 

 has been confirmed for C. virginica and C. gigas. 

 At room temperature of 21° to 22° C. the crystal- 

 line styles of the American species removed from 

 the sac and left exposed to air completely dissolve 

 wdthin 45 to 60 minutes. In the body of the 

 oysters {C. virginica) taken out of water the style 

 disappears in 2 to 3 hours. The absence of the 

 style is frequently observed in nonfeeding oysters. 

 The symptom is useful, but not entirely reliable 

 because under certain conditions the style may be 

 present in oysters which do not take food. Ob- 



servations made in winter in the Woods Hole 

 laboratory showed that in late December, at tem- 

 peratures varying from 5.4° to 5.7° C. about 4 out 

 of 10 oysters had crystalline styles. No trace of 

 food was found in these oysters, which were ex- 

 amined within a few minutes after they had been 

 taken out of water. 



Yonge (1926a) states that in 0. edulis the style 

 is always present in healthy oysters, even when 

 they are starved, and is absent only under ab- 

 normal conditions and in diseased specimens. 



The style must be the product of secretion but 

 investigators do not agree on the manner and site 

 of its formation. List (1902), Nelson (1918), 

 Edmondson (1920), and Mackintosh (1925) think 

 that the style is secreted by the narrow cells of the 

 smaller typhlosoles but do not present conclusive 

 evidence in support of this view. For fresh- 

 water Anodonta, Gutheil (1912) demonstrated the 

 presence of vesicular granules around the nuclei 

 of the epithelial cells of the sac and probably 

 interpreted them correctly as a sign of active 

 secretion. No such granules were found, however, 

 in the histological preparations of 0. edulis (Yonge, 

 1926a) and in my slides of the sac of C. virginica. 

 Evidence of the secretory activity of the style sac 

 was produced by Yonge (1926a) by injecting 0.5 

 percent solution of iron saccharate into the ad- 

 ductor muscle, washing the animals, and then 

 dissecting and fixing the sac at 2-hour intervals. 

 The sections were treated by potassium ferricy- 

 anide in acid solution to demonstrate the presence 

 of iron by Prussian blue reaction. Fine blue 

 granules indicative of the presence of iron salt were 

 found in the cytoplasm above the nuclei and be- 

 tween the cilia of the epithelial cells. No iron 

 was detected in the epithelium of the midgut or 

 of the larger typhlosoles, although some of the 

 metal was present in the epithelial cells of the 

 minor typhlosole. The experiments may indicate 

 the secretory function of the epithelial cells, but 

 they cannot be considered as evidence of the 

 formation of the style from the secreted granules. 



CHEMICAL COMPOSITION 



Analysis of the crystalline style of Cardium 

 made by Barrois (1889, 1890) showed the following 

 composition: water 87.11 percent; solid organic 

 matter 12.03 percent; sohd inorganic matter 0.86 

 percent. The organic component of the style was 

 considered to be a globulin with traces of mucus 

 or chondrinlike substance. Berkeley (1935) dem- 



ORGANS OF DIGESTION AND FOOD OF THE OYSTER 



225 



