GENUS S TEN TOR. 



591 



viously known to Trembley and Baker, the present specific title of this animalcule 

 was conferred upon it by O. F. Miiller in the year 1773, who figured and described 

 it under the name of VorticcUa polymorpjms. Not unfrequently the colonies of this 

 type are found socially inhabiting a common more or less granular gelatinous 

 matrix somewhat resembling that of Ophrydium, but of less substantial consistence. 

 A fragment of such a colony, as observed by the author developed upon 

 the leaves and rootlets of plants of Anacharis in a small aquarium containing 

 axolotls kept in the Zoological Department of the British Museum in the year 

 187 1, is represented at PI. XXX. Fig. 11. Fig. 16 of this plate illustrates a zooid 

 from the same colony as observed in the act of discharging faecal matter from the 

 anal aperture, the matter being shot out with such force as to alight at a consider- 

 able distance. At Fig. 14 an example from the same stock is delineated in which 

 the rudimentary peristomal fringe of a zooid preparatory to dividing by oblique 

 fission presents, at pr, the aspect of a laterally developed membranous crest. 



Stentor Roeselii, Ehr. Pl. XXX. Figs. 22 and 23. 



Body large, the anterior extremity in full extension, scarcely equalling 

 in width one-quarter of the total length ; usually excreting around it and 

 inhabiting an independent, transparent, gelatinous sheath ; parenchyma 

 soft, completely transparent; cuticulum often bearing in addition to the 

 ordinary ciliary covering numerous fine long setae which stand out at a 

 right angle to the surface of the integument, these setae inserted basally 

 in the inner substance of the cortex and extensile or retractile at will • 

 a brush-like fascicle or circlet of fine setae surrounding the adhesive posterior 

 extremity ; endoplast at first serpentine or ribbon-like, subsequently monili- 

 form. Length of extended body 1-24". 



Hab. — Standing water among decaying vegetation ; mostly solitary. 



According to Ehrenberg, the only difference subsisting between this species 

 and the preceding is represented by the form of the nucleus or endoplast, which 

 is described by him as moniliform in Stentor polymorphus., but simply band-like 

 in the present type. This distinction, however, has been shown by Stein to be 

 entirely unreliable, a moniliform contour being assumed likewise by the endoplast 

 of S. Roeselii in the more matured condition of its development. At the same time 

 there are other far more important points of divergence, overlooked by Ehrenberg 

 but pointed out by Stein, which leave no doubt as to the claim held by the present 

 type for independent specific recognition. Among the most prominent distinctive 

 features of the animalcules of the present species, as amended by Stein, may be 

 enumerated the almost invariable presence in connection with their fixed condition 

 of an independent mucilaginous lorica or investing sheath, within the cavity of 

 which they at once retreat upon disturbance ; the presence of the numerous scattered 

 hair-like setae which project from the cortex to a considerable distance beyond 

 the external cuticular surface, and the circlet or brush-like fascicle of finer setse at 

 the posterior extremity. All of these three characteristics are wanting in Stentor 

 polymorphus, and while, on the other hand, fine cuticular setae sometimes occur in 

 S. cceruleus, they attain a much less considerable degree of development, and there 

 is no investing sheath or tuft of caudal setze. This posterior tuft of setae would 

 appear to be subservient to the purpose of anchoring or attaching the animalcule 

 in a root-like manner to the mucilaginous substance of the bottom of its sheath 

 fulfilling the part of the simply adhesive adaptation of the posterior extremity that 

 obtains in various other forms. The presence in this species of supplementary 

 cuticular setas was first observed by Lachmann in the year 1856,* and was well 



* Miiller's ' Archives.' 



