CORRELATION BETWEEN METABOLIC GRADIENTS. 337 



gradient reversed while it was being tested, the aboral pole being 

 first positive and then negative in Nos. 3 and 18 and first negative 

 and then positive in No. 7. In six tests on Bcroe the aboral pole 

 was negative to the oral in three cases, was negative on first read- 

 ings and then became positive in two cases, and in one case there 

 was no definite potential difference between the two poles. It was 

 pointed out above that physiological reversal of the wave in the 

 plate rows is common. 



3. Galvanofaxis. No definite response to current was found in 

 Pleurobrachia, nor to our knowledge has the matter been tested by 

 others. 



VII. FLATWORMS. 



Definite tests of forms belonging to this group were made by 

 Hyman on Planaria inaculata at Woods Hole in 1919 and on an 

 unidentified polyclad turbellarian at Friday Harbor in 1920. 



i. The Metabolic Gradient. This has been studied by members 

 of this laboratory for several species. The anterior end has the 

 highest metabolic rate and this rate decreases along the axis to the 

 level of the main fission plane, beyond which it increases again. 

 It has also been found that the carbon dioxide production (Rob- 

 bins and Child, '20) and the oxygen consumption (Hyman, '23) 

 are higher for anterior than for posterior levels of the first zooid. 

 In Planaria maculata,, tested with potassium cyanide, the following 

 condition was found : The disintegration begins at the anterior end 

 and progresses posteriorly along the margins of the head and the 

 ventral surface ; it then begins at the posterior end and progresses 

 forwards ; the two waves of disintegration meet at about the middle 

 of the worm. There is thus in this species a " double " gradient, 

 from the two ends of the body toward the middle. The high 

 susceptibility of the posterior end is probably due largely to the 

 use of this end as an adhesive organ, less to the presence of a 

 second zooid there. Very small worms possessed the same sus- 

 ceptibility gradient as large worms. The susceptibility gradient of 

 the polyclad was not tested, owing to scarcity of material. 



2. The Electrical Gradient. The data on the metabolic gradient 

 would lead us to expect that the anterior end of Planaria maculata 

 will be negative (galv.) to other levels of the body. This was 



