232 ELIZABETH S. P. REDFIELD 



Bureau of Fisheries for the privilege of working in its Woods 

 Hole Laboratory. 



DESCRIPTION OF THE MOVEMENTS OF THE MANTLE 



If a small hole is cut in the shell of a clam (Unio complanatus), 

 the mantle will bulge out through it. At regular intervals the 

 mantle may be observed to contract rapidly and then to bulge 

 out slowly. To determine the periods of time between these 

 contractions, a small bent needle was hooked through the mantle 

 and attached by a silk thread to an aluminum lever and records 

 were taken on a kymograph. Several species of lamellibranchs 

 were tested and the rate of the rhythm was found to vary in 

 them. It also varied in different individuals of the same spe- 

 cies. In some the period was about one minute, in others about 

 three. In Mya arenaria it was most uniform. The periods 

 lengthen after a clam has been kept in the laboratory for several 

 weeks. It was necessary therefore to use only clams which had 

 been collected within a short time before the tests were made. 



The movement of the mantle might be attributed to changes 

 of pressure within the mantle chamber, produced by the rhythmic 

 movements of the shell, such as Babak has described. In order 

 to determine this point the following experiment was carried 

 out. Simultaneous records were taken of the movements of 

 both the shell and the mantle of a Unio complanatus. Figure 

 1, A, B, shows these movements to be in unison. The parts of 

 the valve of this clam to which the anterior and posterior ad- 

 ductor muscles were attached were now cut free from the rest 

 of the valve, thus allowing the adductor muscles to contract 

 without moving the rest of the valve. Records were again taken 

 simultaneously of the movements of both the shell and mantle 

 (fig. 1, C, D). It is clear from these records that, although the 

 shell was motionless, a slight but distinct contraction of the 

 mantle occurred at regular intervals. 



During the summer of 1915 the movements of the mantle in 

 a number of marine lamellibranchs were studied at the labora- 

 tory of the United States Bureau of Fisheries at Woods Hole, 

 Mass. 



