ANALYSIS OF STENTOR 253 



and usually the major portion of the band was cast off, including 

 both membranelles and a basement ribbon (Fig. 70B). This effect 

 was all or none ; for although only part of the band might be shed, 

 there was no case in which the band was simply injured while 

 remaining in place. When the animals were left in these solutions, 

 the wave of disintegration of the ectoplasm passed over the frontal 

 field and proceeded posteriorly down the lateral surfaces, often 

 being met by a corresponding wave originating in the holdfast and 

 moving forward (b). Hence the appearance was just like that of the 

 disintegration in KCN demonstrated by Child (1914). Again, 

 there was an all or none effect, the ectoplasm becoming totally 

 disintegrated or remaining intact with cilia beating. Even after 

 half the ectoplasm was destroyed, disintegration stopped at once 

 on return to normal medium and the remaining part could still 

 survive and recover. The disintegrated ectoplasm as well as the 

 underlying endoplasm was then pinched off to leave a viable 

 mid-fragment (b). 



It seems odd that the membranelles, with their deep-lying basal 

 plates, should have been the first to go, but this was clearly the case. 

 In fact, urea and sucrose treatments gave very neat shedding of 

 the membranellar band if treatment was stopped promptly, 

 without the frontal field or lateral ectoplasm being affected in any 

 way. Sea water and most of the other treatments caused a lifting 

 of the band first at its distal end. Specimens were often obtained 

 in which the mouthparts remained intact, complete with their 

 membranelles; but in Holtfreter's solution the membranelles fining 

 the gullet and bordering the oral pouch were usually the first to go. 

 Therefore it is possible by choosing the proper treatment to 

 produce specimens in which the mouthparts alone are complete, 

 and others in which only these parts have been subjected to dele- 

 tions. This technique is also convenient for producing large 

 numbers of animals in simultaneous regeneration (p. 353), or for 

 inducing primordium formation in graft complexes without the 

 need for cutting operations which might disturb a contrived 

 arrangement of the lateral striping. 



Oral primordia were also shed in salts, urea, and sugars. The 

 more advanced its development, the more likely was the primor- 

 dium to be shed. Sloughing usually began at the anterior end and 

 proceeded posteriorly. At early stages, on the contrary, in which 



