WATER CURRENT PRODUCED BY ASCIDIA ATRA 



431 



of Spinosella whose volume was ca. 95 cc. discharged 54 cc. per 

 minute through its oscuhim, or about 78 hters a day. 



II 



1. For determining the volume of the current of water gener- 

 ated by Ascidia atra, I adopted a simple indirect method. A 

 glass tube whose bore was a few millimeters less than that of 

 the expanded oral opening, was suddenly introduced into that 

 opening, and the siphon allowed to contract upon it. The tube 

 was then securely tied to the siphon. If an attempt is made to 

 force a tube into a siphon which has begun to close, the mantle 



o , — — 



---''^ c 



Oy ^ 



\ Bo 



O /O 20 JO -40 Jo 60 yo 60 90 /OO /'O /20 /JO A^O /So 



Fig. 1. The volume of sea water passing through different sized specimens of 

 Ascidia atra. 



tissue is always injured, and the animal never recovers from the 

 injury. The velocity of finely divided carmine particles as 

 they passed through the tube into the animal, was determined 

 at frequent intervals, until a maximum velocity was attained. 

 Ten readings were then made and an average taken. Knowing 

 the diameter of the tube and the velocity of the current, the 

 volume of water passed through the tube may be readily 

 calculated. 



A preliminary determination made on an animal ca. 10 cm. 

 long, gave this volume a value of 94.2 cc. per minute. Seven 

 animals of various sizes were then selected, and the volume of 

 the currents measured. The weights of the individuals and the 

 number of cubic centimeters of sea-water passing through in 

 a minute are given in the accompanying figure. 



