240 SELIG HECHT 
TABLE 1 
RANGE DIAMETER ANGLE 
ANIMAL BETWEEN 
Incoming Outgoing Oral Atrial SIEHONS 
mm. mm. mm. mm. 
VI.20.2 5 65 4.0 Peta) 43° 
V1.20.3 12 110 5.5 SHO 65° 
Wale 22 eT 15 230 13.0 6.0 35m 
The oral orifice is large, whereas the atrial is small. Therefore, 
the velocity, and consequently the momentum, of the water in 
the atrial current is greater than in the oral current. The di- 
ameters of the siphon rims of the three animals mentioned are 
given in columns 4 and 5 of table 1. The figures are not very 
accurate, because of the difficulty of maintaining the living animal 
in a constant state of expansion. They show unmistakably, 
however, that the difference in the force of the two currents 
depends, in the main, on the size of the siphon orifices. 
A second significant factor concerned with the separation of 
the two currents is the angle formed by the diverging axes of 
the two expanded siphons. In the last column of table 1, 
this angle is recorded for the same three animals. The individual 
variation in the extent of the divergence of the siphons is sur- 
prising; the net result, however, is that the currents are prevented 
from mixing. The combination of a difference in range with a 
difference in direction of the two streams of the water current 
makes Ascidia independent of the fortuitous movements of the 
surrounding sea. 
2. Feeding 
The stream of seawater which passes through the branchial 
sae of Ascidia brings with it a supply of solid food in the shape 
of plankton organisms. The exact method which is used in the 
collection of these organisms has been the subject of conflicting 
statements. 
Earlier writers, such as Roule (’84), described it as follows. 
The mucus secreted by the endostyle is spread over the inside 
of the branchial sae by the ciliary activity of the gill bars. This 
