GENUS DINOMONAS. 421 



The animalcule, as above characterized, presents in profile an aspect so strikingly 

 suggestive of the body of an ant, with its gibbously inflated posterior and constricted 

 central portion, that a specific title indicative of this likeness is herewith conferred 

 upon it. The generic name of Sterromonas, from oreppos, rigid or unbending, bears 

 reference again to the stiff movements in the water of this as yet single known 

 representative of the genus, and which are chiefly induced by the constantly rigid 

 extension of the longer flagellum. Even when altering its course, the animalcule 

 swings round on its axis, as though on a swivel, without visibly bending its body or 

 this organ in the slightest degree, and which thus seems to more closely resemble 

 a stiff seta than a flagellate appendage. At the same time it would appear that 

 this structure is motile at its free extremity, in a swift vibratory manner as in the 

 Pantostomatous genera Spumclla and Oikomonas. In addition to its normal leisurely 

 progress in a straight line, apparently accomplished by the tremulous motions 

 of the shorter flagellum, this animalcule occasionally darts across the field with 

 remarkable rapidity, and it is probable that under these circumstances, the longer, 

 arcuate flagellum constitutes the chief organ of propulsion. The species possesses 

 prominent adaptive capacities, appearing in equal abundance in artificial infusions 

 of hay in both fresh and salt water. The latter medium, indeed, seemed to prove 

 the more congenial, it attaining in this one only, the larger dimensions of 1-1250" 

 cited in the foregoing diagnosis. An example was observed in one instance to form 

 a spherical encystment, such entrance upon a quiescent condition being preceded 

 by the assumption of an irregular amoeboid shape. The aspect of the zooids of 

 this species considerably resembles that of the natatory conditions of Oikomonas 

 mutabilis, represented at PL XIII. Figs. 57 and 58. Its smaller size, persistency of 

 shape, and possession of two flagella readily distinguish it, however, from that type. 



Under the title of " Flagellaten-rhizopodenartige Protozoen " O. Biitschli has 

 described and figured* a flagellate organism which must perhaps be accepted as a 

 second species of the genus Sterromonas. The contour of this organism in dorsal view 

 is more symmetrical than that of S. formicinus, being subcylindrical, with a slightly 

 narrower anterior extremity; the frontal border is obliquely truncate, a spherical endo- 

 plast is stationed at the anterior extremity, and the contractile vesicle is adjacent to 

 the centre of the right-hand border; the endoplasm is more evenly and finely granulate 

 than in the form just described. Biitschli indicates a single long and apparently 

 stiff, arcuate flagellum at the apical extremity, but it is quite possible a second 

 shorter one exists, which has been overlooked. This form was found in water with 

 decomposing organic substances, in company with Anthophysa vegetans and other 

 flagellate types; the length given is 0-03 mm., or about i'8oo". Observing an 

 example assume an amoeboid state, accompanied by the extension of pseudopodic 

 processes, Biitschli has adopted this amoebiform condition as the mature and adult 

 one, regarding the flagellate monad as its larval or zoospore-like phase. This 

 amoeba-like type he further proposes to identify with the Nuclearia simplex of Cien- 

 kowski. It is evident, however, that this amcebiform organism represented merely 

 that transitory condition of the flagellate monad preceding encystment common to 

 so many members of the Flagellate class, and that it is the flagellum-bearing zooid 

 that must be regarded as the typical expression of the species. Presuming that 

 this animalcule is generically related to S.forwianus, it is here proposed to distinguish 

 it provisionally by the title of Sterromonas Butschlii. 



GENUS VI. DINOMONAS, S. K. 



(Greek, deinos, terrible ; monas.) 



Animalcules free-swimming, ovate or pyriform, soft and plastic, but 

 not metabolic ; flagella two in number, equal or subequal in length, vibra- 

 tile, inserted close to each other at the anterior extremity ; endoplasm 

 transparent, granular ; no eye-like pigment-spot ; oral aperture very expan- 



* ' Zeitschrift fiir Wissenschaftliche Zoologie,' Jan. 1878, p. 269, pi. xiii. fig. 22a. 



