STUDIES OF THE OYSTER DRILL 
105 
animal that is admirably suited for quantitative study. The following is a brief 
account of these studies which has already been published in detail elsewhere 
(Federighi, 1929). Two phases of the response were studied: (1) The relationship 
between the rate of current and the rate of creeping, and (2) the effect of the current 
rate on the rate of turning. 
In these experiments the animals were placed in a trough suspended in a cur- 
rent of water of the turbulent flow type. For the experiments on the rate of creep- 
ing the time necessary for the animal to move one-half inch was taken as a measure 
of the rate of creeping. The rate of turning was determined by tracing the path of 
orientation and recording the time necessary for its orientation, then measuring the 
distance thus traveled with a map measure, and finally recording the number of degrees 
through which the animal had passed. Knowing these, the degrees turned per centi- 
meter of path at each current rate used was obtained. Surface current velocities 
of from 1.25 centimeters to 7.6 centimeters per second were used. These were 
determined by recording the time necessary for uniform bits of cork to travel 5 
inches. Between 15 and 20 readings were taken for each velocity and these averaged. 
At each velocity at least 10 readings for each animal were taken on the rate of creep- 
ing or turning, and the average of these taken as the figure for that velocity. In 
all, 14 animals were used in the study of the effect of the rate of current on the rate 
of creeping and 1 1 for the observations on the relation between current rate and rate 
of turning. 
A summary of these data shows that: (1) Creeping and turning are dependent 
on different mechanisms; (2) the rate of turning — that is, the degrees turned per 
centimeter of path — is a function of the current velocity, and that when plotted 
respectively as effect and intensity the curve obtained follows the usual effect versus 
intensity curve; (3) although the rate of creeping is independent of the current rate, 
the amount of resistance overcome — or the work done — is also a function of the 
current velocity; (4) creeping depends either on the ciliated pedal surface or on mus- 
cular activity, and in either case these are not affected by the flow of fluid past the 
animal; (5) turning depends, apparently, on the parietal musculature of the animal. 
The unequal tension on the two symmetrical parietal muscles, produced by the pull 
of the shell, which in a stream tends to straighten out so that the shell presents the 
least resistance to the flow of water with the foot mass as a pivot, is the stimulus 
which brings about orientation. After the animal has become oriented, there is no 
effect produced on the rate of creeping; the current acts only to keep the animal 
oriented. 
Experiments on the behavior of the drill under the influence of light were without 
results, indicating that under the conditions studied, the drill is not phototropic. 
Aside from any theoretical significance the tropistic behavior of the drill has a 
practical application. The response to currents has doubtlessly a great influence 
on the direction of its movements and its negative geotropism is important in the 
consideration of any means of control and in the success of its spawning. 
CONTROL MEASURES 
The preceding study of the life history, habits, and behavior was undertaken 
in order to devise some means to control Urosalpinx cinerea or at least to prevent 
any further invasion. At this stage the investigator feels very keenly how difficult 
this is. Any problem that involves the control of the number of individuals in a 
species already adapted to its mode of life, already having reached an equilibrium 
