No. 3-] MORPHOLOGY OF THE STENTORS, 491 



doubt that it becomes the highly-refractive "basal seam " that 

 forms so conspicuous a portion of the membranella.^ 



The membranella is generally regarded as having originated 

 by the fusion of cilia, and the ease with which it splits up 

 longitudinally on application of reagents (sec Fig. 8, vi) is 

 held to be evidence of this. Besides, it is possible to homol- 

 ogize every part of the membranella, excepting the connect- 

 ing filament, with parts already present in cilia. Furthermore, 

 there are forms among the Holotricha {e.g. Didiniiivi balbianii 

 and DinopJirya lieberkuehni) in which Schewiakoff ('89) has 

 figured ciliary organs which might fairly be considered as in- 

 cipient membranellas. He thus describes them in Didinitim 

 balbianii (p. 15): "Am Rande des abgestutzten Vorderendes 

 befindet sich ein Kranz ziemlich langer Cilien, welche in kleinen 

 Reihen sehr dicht angeordnet sind. Dieselben erscheinen auf 

 den ersten Blick membranellenartig und an der Spitze zerfasert ; 

 es fallt aber nicht schwer sich zu uberzeugen, dass es einzelne 

 Cilien sind, gewohnlich 6 an der Zahl, welche sehr nahe anein- 

 ander stehen und an der Basis wie verklebt erscheinen." 



The function of the connecting filament, which binds to- 

 gether all the membranellas of the adoral zone, is still very 

 obscure. Brauer ('85), who appears to have been the first to 

 mention the connecting filament, ascribed to it a contractile 

 function, believing that it served to contract the frontal field ; 

 but Schuberg has very properly pointed out that this function 

 is amply provided for by the spiral myonemes of the frontal 

 field. On the other hand, the view that this intraplasmatic 

 apparatus has a nervous function (first suggested by Engel- 

 mann, '80, for the inward prolongation of the cirri of Stylo- 

 nichia) seems probable, but incapable of proof. The connect- 

 ing filament in Stentor, as far as position goes, is admirably 

 adapted to coordinate the action of the membranellse, whose 



1 The " bilamellose " structure of membranellas was first made out by Schuberg 

 ('86) in the membranellse of Btirsaria trimcatella, and was afterwards reported by 

 Biitschli and Schewiakoff ('89, p. 1335), and by Schuberg himself ('90), to be 

 present in those of Stentor. In transverse optical section the appearance is that 

 of two parallel rows of dots — the optical expression of two fibrillated lamellae. 

 I have not been able to make out this structure in the membranellae of S. 

 ceeruleus. 



