EUPLOTES WORCESTERI: I. 303 



exceptions a bristle stands opposite eitlier end of eacli membranella. 

 Tliird, a short row of larger bristles lies along the posterior half of the 

 left margin. These bristles are of about the same size and are spaced 

 about the same as the bristles of the dorsal surface. The arrangement 

 of these sensory bristles of the ventral surface gives further support to 

 the view that the bristles are modified cilia. The resemblance between 

 the row of bristles on the inner side of the adoral zone to what some 

 authors call the paroral or preoral cilia of forms such as Stjionichia and 

 Urostyla is oljvious. The outer row of bristles evidently represents a 

 marginal row of cilia. 



Pellicle. — The body is covered by a thin tough pellicle which is usually 

 very difficult to distinguish from the outer layer of protoplasm. Some 

 specimens, after treatment with a modification of the Golgi metliod, 

 show a quite regular network of wrinlvles in the pellicle. On another 

 "occasion an accident in focusing caused the breaking and partial crushing 

 of a number of stained specimens. The pellicle was then easily distin- 

 guished where it projected beyond the protoplasm at broken edges, and 

 also where it had shrunk and wrinkled on the surface of the body as soon 

 as the slight tension to which it had been subjected was relieved. The 

 pellicle is extremely clear and transparent, and shows no structure. 



The cirri project through openings in the pellicle which are a little 

 larger than the bases of those organs, leaving a narrow space around the 

 base of each cirrus where the protoplasm is unprotected. In one of my 

 cultures great numbers of small amcebse appeared, and I then observed 

 several Euplotes which were attacked by the aanosbEe, the latter thrusting 

 part of the body into the Euplotes through the unprotected space at the 

 base of a cirrus, while half or more of the body remained outside. 



Ectosarc (Plate III). — The ectosarc forms a very definite layer of 

 considerable thickness, which can be distinguished easily in both living 

 and stained specimens. The marked feature of the ectosarc is a single 

 layer of large alveoli filled with clear, homogeneous, and apparently fluid 

 substance. These alveoli, viewed from the surface, give the ectosarc 

 very much the ai^pearance of being composed of cells. (Plate III, figure 

 7.) The walls separating the alveoli are usually very thin, but may 

 contain smaller alveoli of similar nature. Their depth is in most cases 

 almost the thickness of the ectosarc, although it is not uncommon to 

 find two layers of smaller alveoli. The contents of the alveoli stain with 

 Lyons blue, while the walls do not; Lyons -blue used in combination with 

 acetic-carmine gives a very sharp picture of the alveolar structure of the 

 ectosarc. The contents of the alveoli do not shrinlc, nor stain with iron- 

 hffimatoxylin. The alveoli and their contents are evidently of an en- 

 tirely different nature from the ectosarc vacuoles and granules described 

 by Metcalf. although they have much the same appearance. Between the 

 ends of the alveoli and the pellicle is a thin layer of protoplasm, which 

 may contain other very fine alveoli. 



