234 



ELIZABETH S. P. REDFIELD 



observed that the contractions of the two sides are in most cases 

 synchronous. By contracting synchronously the lobes would 

 tend to decrease the size of the infra-branchial chamber and 

 consequently drive some of the water out of it. 



In ten other species of marine lamellibranchs pulsations of 

 the mantle of varying degrees of intensity were noted. In those 



-1 1 1 r 



Fig. 2 Kymographic record of the movements of the mantle of Mya arenaria, 

 the valves of which have been held tightly closed. The upper line (A) is a record 

 taken while the clam was in running water. The second line (B) is a record taken 

 thirty minutes after the water in which the clam was placed had been covered 

 with paraffin oil. It illustrates the accelerated rate which characterizes the early 

 stages of suffocation. The lower line indicates time intervals of thirty seconds 

 each. 



TABLE 1 



The rate of contraction of the mantle and shell of a Mya arenaria kept in running 

 water for three days. Averages are based on counts extending over twenty-minute 

 periods 



First day. . . 

 First day. . . 

 First day. . . 

 Second day 

 Third day. . 

 Third day. . 



9.30 a.m. 

 10.00 a.m. 

 11.00 a.m. 



5.30 p.m. 



6.30 p.m. 



7.15 p.m. 



AVERAGE NUMBER 



OF CONTRACTIONS 



OF MANTLE PER 



MINUTE 



1.3 



1.3 

 1.3 

 0.9 

 0.5 

 0.9 



AVERAGE NUMBER 



OF CONTRACTIONS 



OF SHELL PER 



MINUTE 



0.2 



0.35 



0.1 



0.15 



0.3 



0.25 



Fig. 3 Simultaneous kymographic records of the movements of the right and 

 left mantle lobes of Mya arenaria with the shell tied closed. The top line is a 

 record of the left mantle lobe; the middle line is a record of the right mantle 

 lobe. The bottom line indicates time intervals of thirty seconds each. 



These records illustrate the fact that the two lobes contract synchronously. 



