550 JOHNSON. [Vol. VIII. 



nor less than the ordinary activity incident to regeneration, on 

 whatever occasion it occurs. 



As previously stated (p. 526), the regeneration of membra- 

 ncllae, so far as observed, takes place in only one way — by 

 formation of a new adoral zone on the ventral surface of the 

 animal, normally along the left border of the ramifying zone. 

 Although no definite experiments have been made to ascertain 

 whether nucleate merozoa with no portion of the ramifying 

 zone are able to regenerate the membranellae, certain figures^ 

 and statements of Gruber ('86) and Balbiani ('92) make it very 

 probable that such is the case. In his recent work upon the 

 merotomy of Stentor, Balbiani ('92) implies that a new zone, or 

 at any rate a rudiment of one, is sometimes developed in situ 

 at the anterior end of the merozoon. It appears to me that in 

 some of these cases the early stages of zone-formation were 

 overlooked, while in others the structures taken for mem- 

 branellae are large cilia. I have sometimes noticed a crest of 

 long cilia at the anterior extremity of a merozoon, long before 

 the regeneration of membranellae appeared. 



An experiment, unfortunately a single one of the kind, gave 

 the following interesting result : A Stentor was cut transversely 

 at a point considerably nearer the posterior than the anterior 

 end. A few hours later, the anlage of a new zone appeared on 

 the anterior merozoon. No trace of it had been visible at time 

 of bisection. Believing it to be simply a case of regeneration 

 of the mouth, I paid little attention to it ; but, upon examining 

 the animal two or three hours later I was astonished to find 

 that the new zone was the forerunner of fission. The new 

 mouth was formed in the same place as if the animal were 

 entire, and, therefore, much nearer the posterior end of the 

 merozoon than the anterior. Fission was carried through 

 successfully, giving birth to offspring of very unequal size. An 

 unequal bipartition in 5. ccendeiis is of very rare occurrence ; 

 aside from the above, I have noted but one instance where the 

 daughter-stentors were visibly unequal. The unequal division 

 above noted may then be safely referred to the amputation of 

 the posterior portion of the Stentor. The experiment seems 



^ E.g., Gruber's Fig. 3, merozoa A, C, and Balbiani's Fig. 3, merozoon b. 



