184 



THE AMERICAN MONTHLY 



[October, 



colorless ones are probably amyla- 

 ceous in character, the large, various- 

 ly tinted plates presumably being 

 partially digested food-masses. The 

 nucleus was not determined. It re- 

 mained invisible even after the appli- 

 cation to the body of reagents and 

 staining fluids. 



Dexiotricha centralis, sp. nov. 



(Fig. 3)- 



Body elongate sub-reniform or 

 bean-shaped, longitudinally striate, 

 about twice as long as broad, widest 

 posteriorly, both extremities round- 

 ed ; dorsal surface convex, ventral 

 aspect anteriorly concave ; oval aper- 

 ture ovate, situated somewhat in ad- 

 vance of the centre of the ventral sur- 

 face ; pharyngeal passage short, re- 

 curved ; cilia long and fine, those of 

 the posterior extremity longest and 

 most setose ; caudal seta single, sub- 

 equal to the body in length ; adoral 

 setfe fine, adcurved, extending in a 

 single row obliquely across the right- 

 hand lateral border, from a point 

 posterior to the centre of the dorsal 

 surface to near the centre of the right- 

 hand margin of the oral aperture ; 

 endoplasm colorless, granular, trans- 

 parent : nucleus not observed ; con- 

 tractile vesicle single, spherical, near 

 the posterior extremity. Length of 

 body ^^^ inch. Habitat. — Stagnant 

 pond water, with Leinna and other 

 aquatic plants. 



This is readily distinguished from 

 D. flagia,, Stokes (Amer. Journ. 

 Sc/., April, 1885), by the more pos- 

 terior position of the adoral seta; and 

 of the contractile vesicle, by the much 

 greater proportionate length of the 

 caudal seta, but especially by the en- 

 tire absence of the apparently bi-con- 

 cave corpuscles so abundantly present 

 within the endoplasm of D. plagia. 



As is usually the habit with the 

 last named form, D. centralis when 

 taking food rests upon one side, the 

 cuticular cilia in the rear of the 

 adoral setae then being comparatively 

 quiescent, while those clothing the 

 frontal region are in the most active 

 movement, the currents thus pro- 



duced, in both species, carrying the 

 food-particles against the oblique se- 

 tose hedge which deflects them to- 

 ward the mouth. 



Stentor globator,, sp. nov. (Figs. 

 4 and 5). 



Body subspherical,\changeable in 

 form, free-swinging or temporarily 

 adherent by a long, narrow, retractile 

 tail-like prolongation protruded from 

 the centre of the posterior extremity ; 

 peristome field elevated, rounded, 

 finely ciliated in concentric circles ; 

 cuticular cilia fine, arranged in lon- 

 gitudinal lines, longest posteriorly ; 

 hispid setae long and numerous, ex- 

 tending at right-angles to the general 

 surface ; nucleus not observed ; con- 

 tractile vesicle double, spherical, pos- 

 teriorly located. Diameter of the 

 body -3^^ inch. Habitat. — Still water, 

 with J]/yriop/iylhan. 



This remarkable stentor widely 

 differs from any hitherto observed, 

 possessing some characteristics that 

 will necessitate changes in the generic 

 diagnosis as formulated by Kent. 

 Most members of the genus are noted 

 for the ease with which they change 

 their shape, the alteration, however, 

 being confined chiefly to a contrac- 

 tion and consequent change in the 

 form of the entire body. Several 

 species have been observed with very 

 fine pseudopodic filaments emitted 

 from the posterior extremity, but 

 none, so far as I am aware, have 

 been recorded with the peculiar abili- 

 ty which S. globator possesses of 

 posteriorly protruding a soft, flexible, 

 attenuate tail-like prolongation equal 

 in length to the diameter of the body, 

 to be subsequently entirel}' with- 

 drawn, and again protruded when 

 the exigencies of the situation de- 

 mand. The appearance of this tem- 

 porary caudal prolongation brings to 

 mind a pseudopodic protrusion, since 

 it has the ability to somewhat alter 

 its contour by the formation of several 

 irregularly distributed enlargements 

 which may be speedily absorbed, the 

 part then becoming a long, simple, 

 attenuate prolongation, the extreme 



