PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 239 
for the range of activity of the two currents. In columns 2 and 
3 of table 1 are given the values obtained for two additional 
animals. Record VI.20.3 is of an individual about twice, and 
V1I.22.1 of an individual about four times, the size of the speci- 
men in figure 3. 
20.2 
Fig. 3 Range of the incoming and outgoing streams of the water current. 
The maintenance of such a contrast in the force of the two 
branches of the water current is accomplished by a difference 
in the size of the openings of the oral and atrial siphons. The 
cilia furnish the motive power, and the same quantity of water 
which they move passes through both openings in the same time. 
