CONTRACTIONS IN MANTLE — LAMELLIBRANCHS 235 



forms which are sedentary, the rhythmic movements were found 

 to be much as in Mya arenaria. Such forms were Modiolus 

 modiohis, Modiolus plicatula, and Mytilus edulis. The last 

 showed only weak movements. In the forms which were active, 

 such as Solemya velum, Ensis directis, Cummingia tellinoides, 

 and Yoldia sapotilla, there are also movements of the mantle 

 perhaps respiratory in function, but somewhat different from 

 those in Mya. In Pecten gibbus, Venus mercenaria, and Ostrea 

 virginica the mantle is very thin and in close connection with 

 the shell. No movements of the mantle were discovered in 

 these forms. The gills in the last three are more active than 

 those in the others, which may be of significance. 



THE FUNCTION OF THE MOVEMENTS OF THE MANTLE 



To determine whether the movements of the mantle were 

 concerned with setting up the respii-atory currents in the infra- 

 branchial chamber, the effect of suffocation upon the rate of 

 the rhythm was determined. Specimens of Mya, placed in a 

 bowl of running sea-water, were attached to the recording appa- 

 ratus and the rate of the mantle pulsations determined. The 

 water was then covered with a thin layer of paraffin oil.^ As 

 the oxygen in the water became exhausted the rate of the rhythm 

 increased rapidl> (fig. 2), but as the movements proceeded this 

 rate fell off, the movements stopping completely before the 

 clam succumbed. Figure 4 is a graphic representation of the 

 changes in the rate of movements of the mantle of Mya arenaria 

 during suffocation. 



If, as the foregoing facts suggest, the mantle movements are 

 concerned with setting up respiratory currents, it might be 

 expected that an obstruction of these movements would influ- 

 ence the quantity of oxygen consumed by the clam. Accord- 

 ingly experimentis were carried out in which the oxygen consump- 



1 Bayliss ('15) has pointed out the futility of attempting to preserve solutions 

 from the action of gases in the atmosphere by covering them with oil or hydro- 

 carbons. This observation does not invalidate the results of the experiments 

 in question since the animals died of suffocation, though perhaps no more rapidly 

 than if the surface of the water had not been covered with paraffin oil. 



