42 THE BIOLOGY OF STENTOR 



in Spirostomuniy in which also the new vacuole is produced at 

 division simply by an enlargement of this canal. Anterior to the 

 new vacuole a segment of the longitudinal canal separates both 

 from this vacuole and from the posterior end of the anterior 

 daughter, producing the circumoral " ring canal " discovered by 

 Lachmann (Claparede and Lachmann, 1 858-1861) ; but this 

 severed portion of the canal soon atrophies and hence is seen only 

 in the young opisthe. Haye stated that polymorphus also has a 

 longitudinal canal but he did not describe or illustrate it. In 

 coenileus Andrews saw many channels emanating from the 

 contractile vacuole. One proceeded forward and led to a horizontal 

 ring canal underlying the frontal field ; others proceeded backward 

 toward the foot and from such might come the new contractile 

 vacuole during fission. 



5. Cortical structure 



The well-differentiated cortex or ectoplasm of Stentor is highly 

 extensible, considerably elastic, sharply contractile, capable in 

 part of being shed and regenerated, as well as bearing cilia with 

 the means of their coordination. These properties and functions 

 are to be related to the types of microscopic and submicroscopic 

 structure present. Even today our knowledge of this correlation 

 is still highly problematical; nor is it certain that all structural 

 details have been revealed, though electron microscopy has made 

 possible astonishing advances in this study. 



From the standpoint of morphogenesis, the cell cortex with its 

 enduring pattern is of greatest importance. For it is from this layer 

 that other cytoplasmic organelles are elaborated, as when a mid- 

 section fragment regenerates a new head and foot. As will become 

 evident later, both holdfast and oral primordium formation are 

 intimately related to the polarity and pattern of the cortex, and 

 we may hope that the causal basis of this relationship will in time 

 be exposed. 



(a) The cell surface 



Proceeding from the exterior, there is a pellicle, long ago 

 demonstrated by Johnson who saw it lift off the cell on treatment 

 with weak osmic acid while remaining firmly attached to the ciliary 

 rows. Electronmicrographs of Randall and Jackson showed the 



