DIFFERENTIAL INHIBITION IN OBELIA 487 



are ingested by the endoderm cells of the hydrocaulus, or break 

 down and in that condition are absorbed by those cells. 



The walls of the hydrocaulus even in the last stages of resorp- 

 tion appear normal when seen alive under the microscope and 

 in sections, though its cavity may be filled up with cells and 

 debris. 



But is it possible that the new growth which takes place at 

 the proximal cut end of the hydrocaulus consists of the very 

 elements derived from the resorbed zooids ? Loeb makes -the 

 observation that this growth is like the motion of a protoplasmic 

 mass, and such it certainly appears to be in our experiments. 

 But this would be the appearance presented by normal growth 

 proceeding at the rate at which this stolon was produced — 

 10 mm. in forty-eight hours or less. 



In structure the new growth is similar to an ordinary piece 

 of hydrocaulus (Text-fig. 3). 



This growth starts only after a certain stage of resorption 

 has been reached. 



The new growth adheres to the substratum, thus resembling 

 the normal creeping stolon. We were unable to observe whether 

 it could give rise to buds in Obelia, as the preparations died. 

 In Campanularia, pieces with several zooids might give rise 

 to one or several buds during or after resorption of the original 

 zooid. 



Discussion. 



Loeb (1900) attributes resorption to contact with solid 

 objects. According to him the transformation must be due to 

 liquefaction of the more solid constituents of the zooid. Con- 

 tact with the fluid, sea-water, makes for the production of the 

 more solid portion of the colony, the zooid ; whereas con- 

 versely contact with a hard surface makes for the more fluid 

 stem. Accordingly if a zooid be subjected to the stimulus to 

 which the production of the stem-system is the reaction, the 

 result will be the conversion of the zooid into something 

 resembling the stem. ' 



But resorption of zooids takes place even when the colony 

 is maintained in an erect position and no portion of the zooid 



K k2 



