No. 3.] 



MORPHOLOGY OF THE STENTORS. 



505 



dinal canal by the separation of the daughter-stentors — or 

 possibly somewhat earlier. Within a few hours after fission, 

 the ring canal atrophies without leaving a trace. It is evident, 

 then, that Lachmann saw the ring-canal in a young specimen 

 of 5. roeselii, and later observers have for the most part failed 

 to find it because they did not obtain young specimens. 



As soon as the new zone has reached its full length, has 

 curved inward at the ends, and its membranellae have attained 



..c/.' 



-CV" 



Ac'. 





Fig. II. — Diagrams to illustrate the formation of the ring canal in S. roeselii. 

 CV., contractile vacuole ; cv.,^ new contractile vacuole ; Ic, Ic.,^ longitudinal canal •, 

 re, ring-canal. 



a definite shape, the new pharynx begins to develop (Figs. 27, 

 28,^.1). It starts as a slight depression in the body of the 

 Stentor just at the posterior tip of the new zone. The first 

 direction taken is obliquely inward towards the right. The 

 invagination becomes deeper and larger, then turns spirally 

 and pushes directly into the endoplasm (Fig. 13 ^.^ inv.). The 

 tip of the new zone follows the invagination pari passu, so 

 closely as to give the impression that the zone is pushing into 



