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peristome margin with its thick set cilia makes a right-handed spiral with more than one turn." Stein considers that the Stentors may either stand as a separate family, or be united with Freia in a family constructed upon a different plan to that of any other heterotrichal infusoria. In Freia the mouth end is divided into two ear-like projections, and the spiral twist runs deep down in the funnel-shaped portion. There are obvious points of resemblance between the Stentors and the Vorticellina and Ophydium, but the differences are still more important. The peristome of the two latter is constructed on a different type, the peristome field projects above the margin, and can be drawn in and out; the oral cilia form a left-handed spiral. The bodies of Stentor and Freia are moreover covered with cilia, and exhibit longitudinal bands.
The general aspect of the Stentors in different positions, witlı their principal organs, will be readily apprehended by reference to Plate I. given with this number, and to Plate II., which will appear with the next number. In Plate I., Fig. 2, the peristome field, r, is seen surrounded by the oral cilia, which are interrupted on the ventral side, and form two curved portions distinguishable as right and left bends. The right bend has its free end directed inwards, towards the axis of the body. The left bend is curled towards the mouth. Stein calls the termination of the left bend the peristomeck or peristome corner. From this peristome corner the ciliary zone is of uniform breadth to the beginning of the right bend, when it gradually narrows, and the part surrounding the mouth is merely a rounded line. When not in use the mouth-cilia are retracted and lie in the furrows, shown in Plate I., Fig. 2, r.
When a Stentor attaches itself by its tail end, Stein says it does not do so by any sucker, as no such apparatus is provided, but by means of fine pseudopodia with projections put forth from the body for the purpose. Sometimes a small depression may be seen at this end, as shown in Plate I., Fig. 10, but usually it is rounded off. The pseudopodic projections have the appearance of a wreath of long bristle-like cilia, and are shown in Plate II., Fig. 2, f. When free swimming, no such projections appear.
The pocket-shaped hollow in which the mouth is situate, is shown, Plate I., Fig. 1,t, being the depression, and o, the mouth. The mouth leads into a short, thin-walled, tubular, contracted, or bent gullet, Plate I., Fig. 9, 8. It is directed obliquely inwards and backwards, and, like the mouth, is capable of considerable extension. The oral cilia are directed into the gullet, and form a long drawn spiral reaching to its extremity. The gullet or esophagal cilia are VOL. III.-N0. V.