186 



THE AMERICAN MONTHLY 



[October 



accomplished rapidly. If this caudal 

 prolongation is present, the convex 

 peristome-field is conspicuously flat- 

 tened, the body is narrowed and 

 lengthened, and only at this time 

 does the infusorian present any re- 

 semblance to the trumpet-like form 

 so commonly assumed by other mem- 

 bers of the genus. The entire body 

 is soft and changeable in shape. 

 Even when the tail-like part is not 

 protruded, the infusorian then being 

 a free - swimming animalcule, the 

 changes are quite marked and ex- 

 tensive. 



That the peristome field of Stentor 

 is ciliated I have not personally ob- 

 served in any other species except 

 Stentor polvmorphus and 6'. Bar- 

 rettz\ in which the condition obtains, 

 nor have I been able to find that 

 such a state of the part has been noticed 

 or recorded. It is probable that the 

 peristome field is ciliated in all the 

 species, but that it has not been re- 

 corded is somewhat difficult to under- 

 stand. In^ Stentor globator^ how- 

 ever, the ciliation is conspicuous. 

 The peristome field is furrowed by 

 concentric lines, fine cilia clothing 

 the depressions. The nearest re- 

 corded approach to this condition 

 is found in S. fediculati<s^ From., 

 in which the peristome field gives 

 origin to numerous papilke bearing 

 fine non-vibratile setaj. 



The cirri composing the peristomal 

 fringe are large and numerous. When 

 at rest each one presents an appear- 

 ance remotely similar to that of the 

 adoral ciliary wreath in Tintlnnidi- 

 um. se7niciliat2ini^ where each cilium 

 is distally pectinated. After careful 

 scrutiny, however, I have been un- 

 able to demonstrate the existence of 

 such a structure. The appearance is 

 probably due to a confused image of 

 the intermingling adoral cirri and the 

 finer cilia of the peristome field. The 

 last named part is much more convex 

 and more elevated than in .Steutor 

 generally, and the infusorian seems 

 to have the amount of convexity 

 under quite complete control. 



The cuticular setae are long and 

 numerous. They are more conspic- 

 uous and apparently more abundant 

 anteriorly than on the posterior parts. 

 They also seem to vary in length in 

 the same row, but the appearance 

 may be due to the convexity of the 

 cuticular surface. They may be ex- 

 tensile and retractile, but this I have 

 not noticed. 



The double spherical contractile 

 vesicles are uncommon in the genus. 

 Their existence in the present species 

 would afiord a ready clue to its iden- 

 tification, if anything more were 

 needed than the peculiar form of the 

 body and the characteristic changes 

 of the posterior extremity. 



In figure 4 is shown the globular 

 body ; in figure 5 the outline of the 

 protruded tail-like prolongation. 



Strombidinopsis setig'era^ sp. 

 nov. (Fig. 6). 



Body ob-conical, twice as long as 

 broad, finely striate longitudinally ; 

 widest at the frontal border beneath 

 w^hich it is constricted, tapering thence 

 to the rounded posterior extremity ; 

 peristomal cilia abundant, curving 

 outw^ardly, their length not exceeding 

 one-half the greatest width of the 

 body ; a series of fine, outwardly di- 

 rected, hair-like setae projecting from 

 the cuticular surface behind the peri- 

 stome border, their length equaling 

 one-half the length of the zooid ; 

 pharyngeal passage wide, ciliate, ex- 

 tending to the centre of one lateral 

 body margin ; endoplasm colorless, 

 transparent ; contractile vesicle single, 

 spherical, posteriorly located. Length 

 of body ^^; inch. Habitat. — Pond 

 water. 



This differs from S.gyrans^ S. K., 

 from English waters, the previously 

 only known species, chiefly in the 

 shortness of the peristomal cilia and 

 the length and presence of the fine 

 setae springing from the anterior sur- 

 face. Its movements are rapid and 

 erratic. It has the habit of frequently 

 darting backward for a short dis- 

 tance, at the same time contracting 

 the frontal portion and partially 



