100 THURLOW C. NELSON 



activity of the mollu.sc, as well as its general physiological con- 

 dition. External conditions, principally temperature, also cause 

 considerable variation in the time required.^ 



Upon dissolution the style forms a brown viscous fluid, most 

 of which remains in the style sac until the animal again begins 

 active feeding, when it is carried forward into the stomach by the 

 active beating of the cilia. 



From the above experiments it may be concluded that the 

 crystalline style is a structure intimately connected with the 

 feeding activities of the mollusc, and which, in oysters exposed 

 at low tide, is completely dissolved and renewed again at least 

 twice every twenty-four hours. 



The style of Modiolus is much more resistant and ordinarily 

 remains intact during the normal periods of inactivity. If mus- 

 sels are kept in the laboratory without food, the style begins to 

 disappear after about twelve hours, and is usually completely 

 dissolved after twenty-four hours of inactivity, though here 

 again there is great variation between individuals. 



The fresh-water genera, Anodonta and Lampsilis, exhibit a 

 condition similar to that of Modiolus. Absence of food or inac- 

 tivity of the animal due to cold or adverse conditions brings 

 about a gradual dissolution of the style, occupying from a few 

 hours to several days. 



The disappearance of the style in forms which had long been 

 out of water was noted by Meckel ('29) and by a number of 

 other workers. Mitra ('01) believed this disappearance and 

 subsequent renewal to be a periodic function. As Allen ('14, p. 

 136) has justly pointed out, this periodicity was due to the 

 periodic emptying and filling of the aquarium in which the ani- 

 mals were kept. The latter investigator also gives the correct 

 interpretation of the presence or absence of the style, and showed 

 that the addition of food to the water containing starved mussels 

 soon caused its partial regeneration. 



We have already seen (p. 80) that the cilia of the style sac 

 put the style into rotation while pushing it forward into the 



^ The rapid dissolution of the style of the oyster was noted by Mobius ('83) 

 and later by Barrois ('89). Garner ('41) even went so far as to hold that with 

 but few exceptions the style was lacking in all of the Monomyaria. 



