No. 3j MORPHOLOGY OF THE STENTORS. 523 



39 A was reached at 12.30 p.m., and that of Fig. 39 B at 2 

 P.M. A fact worthy of notice is that as soon as the second 

 new mouth {p.-) was developed the first {0.'^) began to atrophy, 

 and also the newly-formed membranellae of a.z.^ between the 

 junction of a.z.- with it and the mouth. Points of difference 

 between this double regeneration and an ordinary one were 

 the well-marked places of junction between older and newer 

 adoral zones, and the slowness with which the process was 

 completed. Twenty-four hours after the stage shown in Fig. 

 39 B, the new mouth had not quite reached its normal place. 



As if to show the close connection existing between regen- 

 eration and fission, a Stentor that has started to renew its oral 

 organs may undergo fission instead. I have only once observed 

 it. When first seen, the new zone had already joined the old. 

 I noticed, however, that a new contractile vacuole had appeared 

 in the same place as in fission. Presently I noticed that the 

 most anterior membranellae of the new zone were becomine: 

 smaller. They soon atrophied entirely for about one-fourth 

 the length of the new zone, and only a streak on the pellicula 

 indicated where the zone had previously extended. The mega- 

 nuclear phases were watched, and have already been described 

 (Fig. 47). The subsequent cytopbsmic changes proceeded 

 normally. Within the new ramifying zone of the distal zooid 

 a curious derangement of the stripes was observed (Fig. 40), 

 undoubtedly due to the atrophy of the anterior portion of the 

 adoral zone. 



The time required by the process of regeneration varies in 

 different individuals and doubtless at different temperatures. 

 At i6°-20° C. I have found it requires 6>^ to 8 hours. It is, 

 therefore, a little slower than fission. 



2, Nuclear Phases. 



Balbiani ('9i) calls attention to the interesting fact that the 

 meganucleus goes through precisely the same changes in 

 regeneration of the oral organs as in fission, with the excep- 

 tion that division normally occurs only in the latter instance. 

 But I find him at error in the statement that the number of 

 nodes is not increased at time of retreneration. I have made 



