28 THE ELEMENTARY NERVOUS SYSTEM 



positions favorable for this form of response for over a 

 day. Nor have fingers been observed to turn in con- 

 formity to the direction of the general current of water 

 in which the sponge was standing. In some instances the 

 fingers of Stylotella are not directed straight upward, but 

 their tips are turned to one side or the other so that their 

 oscula open laterally. A number of these sponges were 

 set, some with their oscula facing the general current, 

 others with these openings away from the current, and 

 still others sidewise to the current. After three days 

 none of these had noticeably changed their directions, 

 thus giving no evidence of a general movement of the 

 body. 



Attempts were also made to get evidence of the gen- 

 eral movement of Stylotella through geotropic stimula- 

 tion. This sponge ordinarily grows with its fingers and 

 oscula directed upward, as though it were negatively 

 geotropic. A large colony was, therefore, kept inverted 

 in an aquarium, of circulating seawater for about a week 

 on the assumption that the fingers might be brought to 

 turn from this unusual position, but at the end of this 

 period there was no discoverable change of position. 

 This observation, however, does not prove that Stylo- 

 tella is not geotropic. Slight evidence of its geotropism 

 is to be found in its method of regenerating oscula. When 

 a moderately long finger of Stylotella is cut off and the 

 Avhole of its oscular end removed, the cylindrical body 

 thus resulting will under favorable conditions form a new 

 osculum. Whether this regeneration will take place at 

 the end nearer or farther from the former osculum seems 

 to depend chiefly on the position of the piece of sponge 

 with reference to gravity. If the end that was nearer 

 the former osculum is uppermost, it always regenerates 



