298 ORDER FLAGELLATA-PANTOSTOMATA. 



The genus Spiromonas, as comprehended in this treatise, includes the Cyclidium 

 distortum of Dujardin and Spiromonas volubilis of Perty, to which is added a third 

 very distinct species apparently identical with the Heteromita angustata of the 

 first-named investigator, whose developmental phenomena have been recently traced 

 by the author. The two previously mentioned forms have been regarded by some 

 authorities as possibly representing transitional conditions only of Monas lens, but 

 such an interpretation cannot be entertained in face of the data here recorded 

 concerning the entire life of that species. The members of this genus, as 

 originally described by Dujardin, are represented as having a single flagellum only, 

 while Perty indicates the possession of no appendage whatever. The comparatively 

 inferior quality of the optical appliances at the disposal of these earlier investigators, 

 however, amply accounts for such an oversight. 



Spiromonas distortum, Duj. sp. Pl, XX. Fig. 23. 



Body oval, compressed and nodular, with thickened tuberculate 

 margins, twisted irregularly on its longitudinal axis in a single spire. 

 Length i-iooo". 



Hab. — Fresh water containing decomposing animal matter. 



This species, which is described by Dujardin under the name of Cyclidium 

 distortum, is represented as bearing a single long and slender flagellum at its 

 anterior extremity, though probably a second one exists. The young zooids were 

 observed by him to be simply discoidal, the spiral flexure being characteristic only 

 of the adult animalcules. 



Spiromonas volubilis, Perty. 



Body leaf-like, compressed, rounded at both extremities, twisted longi- 

 tudinally in a single spire ; surface smooth, the margins not thickened or 

 tuberculate. Length 1-1300". 



Hab. — Stale water with decomposing matter in suspension. 



Spiromonas angustata, Duj. sp. Pl. XV. Figs. 49-60. 



Body elongate, linear, compressed, more or less pointed at the two 

 extremities, five or six times as long as broad, twisted spirally or in a 

 screw-like manner on its longitudinal axis ; flagella slender, subequal, 

 inserted close to each other at the apex of the anterior extremity, equalling 

 the body in length, both directed forwards and vibratile when the ani- 

 malcule is swimming, the inferior one sometimes used for the temporary 

 attachment of the animalcule ; contractile vesicle posteriorly located ; 

 endoplast inconspicuous. Length of body 1-2500". 



Hab. — Vegetable infusions. 



The animalcule as above characterized and here identified with the Heteromita 

 angustata of Dujardin, was obtained abundantly by the author at St. Heliers, Jersey, 

 in an infusion of hay with spring water at the end of three weeks' maceration. 

 Although the elongate, screw-like form, with two or three spiral twists, represents 

 the normal aspect of the adult individuals in their free-swimming state, a very 

 considerable range of variation occurs among the units of a large series. This 

 individual variation is dependent not only on the phase of development of the 

 separate monads, but also on the condition of rest or activity that may at the time 

 predominate. In common with Spiromonas distortum, the young of this species 



