492 JOHNSON. [Vol. VIII. 



uniform vibration is essential to the production of an alimentary 

 vortex. 



The Foot, or organ of attachment, is beautifully adapted for 

 anchoring the animal while it expands its frontal field. At- 

 tachment is accomplished, not by means of a "sucker" as 

 believed by Stein and all the earlier writers, but by pseudo- 

 podia protruded from the naked disc of endoplasm (Figs. 14, 

 15, 16). The extent of protrusion and consequently the whole 

 aspect of the foot depends upon the nature of the substance to 

 which the animal is affixed. Thus Fig. 16 shows the foot of 

 5. polymorpJuis attached to glass; pseudopodia are not pro- 

 truded, but the whole foot is simply flattened against the glass, 

 and sticks to it apparently by virtue of the intrinsic adhesive- 

 ness of the protoplasm. Fig. 15 is a sketch of the foot of 

 S. roeselii fixed in loose and flacculent detritus. Spine-like 

 pseudopodia are protruded in all directions; they are mostly 

 unbranched. Fig. 14 represents the very beautiful, ramose 

 pseudopodia of a Blue Stentor affixed to the surface film of 

 water (in this case covered with a very thin bacterial zoogloea). 

 Although the figures are taken from three species, the aspect 

 of the foot represented by each, together with an almost infi- 

 nite series of intermediate forms, may be found in any one 

 species. 



A Stentor never becomes attached until the "stalk" is well 

 protruded from the body. If the foot be carefully watched 

 when the animal is preparing to affix itself, numerous minute 

 processes in rapid vibration will be seen. These bear the 

 closest resemblance to cilia ; indeed, I have often been unable 

 to distinguish, so far as the form of the structures is concerned, 

 where the ciliary covering of the body ends, and the pseudo- 

 cilia of the foot begin. They offer an interesting case of a 

 ciliary organ on naked protoplasm. These minute processes 

 are in all probability highly sensitive, and enable the animal 

 to feel for a suitable place of attachment. Stentors appear to 

 experience difficulty in fastening on clean glass. I have often 

 watched one fully extended, dragging its foot over the under 

 surface of a cover-glass before being able to fasten upon it. 

 If a number of Stentors are put in a glass dish of water, very 



