216 



STUDIES IN GENERAL PHYSIOLOGY 



Hydroid, Hydra, should conduct itself, so far as known, as 

 a strictly "polarized" animal, might render it still more 

 probable that heteromorphosis is simply a characteristic of 

 "colony-forming" Hydrozoa. To settle this question I made 



experiments upon Ciona in- 

 testinalis, a solitary Ascidian. 

 The Ascidians, as is well 

 known, stand near the verte- 

 brates in the animal scale. 



In Fig. 54 is shown in 

 almost natural size the exter- 



FIG. 55 



FIG. 56 



FIG. 54 



nal form of a Ciona intestinalis. a is the oral opening, b 

 the excretory opening, c the foot, which, like the foot of the 

 Hydrozoa, attaches the animal to the surface of solid bodies. 

 At the outer edge of both tubes are situated the ocellse, 

 which are just visible to the naked eye (Fig. 55). The fol- 

 lowing experiments deal with the formation of these ocellse. 

 If the animal behaved like a purely "polarized animal," such 

 as Cerianthus, then, when a lateral incision cba (Fig. 56) is 

 made into it, ocellse should be formed only along the lower 

 cut edge 6c, just as the tentacles are formed only along the 

 lower cut edge of Cerianthus. But the opposite occurs in 

 Ciona. After a short time ocellse (indicated by points in the 

 drawing) are formed along both edges of the wound (ab and 



