No. 3.] MORPHOLOGY OF THE STENTORS. 493 



few affix themselves to the sides of the dish until the glass has 

 become coated with slime. 



The Nuclei. 



Megamicleus . — The three principal forms in which the 

 meganucleus of the Ciliata occurs — the spherical or oval, the 

 vermiform, and the moniliform — are present among the Sten- 

 tors. All the lower forms (S. igneus, S. multiformis, S. niger 

 and 5. pyriformis) have simple, rounded meganuclei. The 

 higher forms {S. auricula, S. ccenilcus, S. polymorphus, and 

 sometimes 5. roeselii) have moniliform nuclei. ^. roeselii 

 retains the vermiform nucleus for a long time after fission, 

 but the moniliform condition is eventually attained. 



The spherical meganucleus is evidently the primitive form, 

 and the vermiform and moniliform shapes are derived from it. 

 The stages of what must have been its phylogenetic develop- 

 ment are repeated at every fission. The vermiform nucleus 

 is not permanent among the Stentors. Even in 5. roeselii, 

 where it is of such frequent occurrence as to have been taken 

 for a diagnostic feature by Ehrenberg ('38) and even by Stein 

 ('67), it appears to be only a transient condition, readily passing 

 into the moniliform state if a considerable time elapses between 

 periods of fission (Fig. 4, mgn.). 



The moniliform nuclei differ but slightly from one species to 

 another. The meganucleus of S. roeselii is peculiar in that 

 the anterior nodes are the thickest and largest, while the 

 smaller posterior ones are long and spindle-shaped (Fig. 4). 

 This results from the shape of the vermiform nucleus, which 

 is always thickest anteriorly. Although the size and shape of 

 the nodes vary considerably in 5. ccsruleus, and also the length 

 and thickness of the commissures, I have but rarely noted any 

 marked deviation from the typical form. One of these was 

 an imperfectly-noded nucleus of a small individual (Fig. 17), 

 which had but three well-defined constrictions, producing four 

 elongated, unequal nodes, two of which showed indistinct con- 

 strictions indicating where commissures would normally be. 

 The condition is evidently one of arrested development, for 

 such imperfectly-noded nuclei are by no means rare at the 



