EXPERIMENTAL STUDY OF THE OYSTER GILL 



ss 



shell open during a day is 17 hours 7 minutes; the median is 18 hours 5 minutes. In 

 a preliminary paper published in 1926 (Galtsoff, 1926) it was stated that the average 

 period of time the shells of an oyster arc open during a day is 20 hours. Nelson 

 (1921), analyzing the records of 3 oysters kept under observation for 21 days, also 

 states that on the average the oysters were open for 20 hours. The present investi- 

 gation, based on more numerous observations, shows that the average period of time 

 when the shells are open is smaller. The decrease of the average from 20 to 17 hoiu-s 

 and 7 minutes is due to a few instances where the oysters failed to open during the 

 24-hour period. 



 An analysis of the records shows that when the shells are open the adductor mus- 

 cle contracts and relaxes periodically. The contraction is often so shght that it 

 does not result in a complete closing of the shell (fig. 11) and is of brief duration, 

 the muscle beginning to relax immediately after the maximum contraction is reached. 

 It has been shown by several investigators that by periodical contractions the 



NI6HT—7 



1P.M. 



Fig. 11.— Part of the record of shell movements of two oysters made at 16° C. 



the pens when shells are closed 



1A.M. 



Dotted lines indicate the position of 



oysters cleanse themselves and discharge the material that had accumulated in 

 the paUial cavity. Although by this reaction the organism is able to get rid of the 

 material accumulated by the gills, the inference that every contraction of the muscle 

 is an ejection reaction is incorrect. Nelson (1921, p. 343) states that from observa- 

 tion of the extent and frequency of the down strokes made by the oysters on the 

 recording apparatus and representing the contraction of the adductor muscle, 

 together with a knowledge of the turbidity of the water, it is possible to determine 

 the rate of feeding. Employing this method he arrives at the erroneous conclusion 

 (1921, p. 339) that "temperature within the Umits observed during the experiment 

 (69° to 90° F.) apparently did not operate as an independent factor in controlhng 

 the intake of food." It has been shown in this paper that the ciliary motion, which 

 is responsible for the intake of food by the oyster, is a function of temperature. The 

 number of contractions of the adductor muscle can not be regarded as an index 

 of the rate of feeding, because the oyster may respond to any external or internal 



