GENUS Z YGOSELMIS. 4 1 ^ 



such discovery justifying its reinstatement as a well-marked generic form. In addition 

 to the two long, equal, vibratile flagella, which were in all normal conditions distinctly 

 seen, the peculiar and rapid peristaltic movements exhibited by the animalcule during 

 its repent state, distinguish it in a marked manner from the various species otEuglena 

 and approximate it more nearly in this respect with the members of the genus 

 Distigma or the essentially repent protozoic type Gregarina. In the examples 

 examined, it was noted that very soon after their transfer to the object-slide they 

 abandoned their natatory for the repent mode of progress, which is possibly the 

 more general and congenial. Encysted conditions were frequently observed, and 

 also the breaking up of the contents of the encysted zooids into innumerable sporular 

 bodies which were subsequently liberated in the form of minute, green, non-flagellate 

 amoebae, these phenomena corresponding with those already recorded of Euglena 

 viridis. Prior to their acquirement of the typical adult state, it is worthy of note 

 that the amoebiform germs possess a single flagellate appendage only, being under 

 such conditions altogether indistinguishable from minute Euglena. 



As compared with Perty's original figures, the animalcules of Eutreptia were not 

 observed during their natatory state to assume so attenuately pyriform a contour 

 as he delineates, the pointed caudal prolongation in the Jersey specimens rarely 

 exceeding one-half of the length of the inflated body-portion, while in the former 

 case it frequently equals or even exceeds this region in length. Perty's so-called 

 variety unifilis of this species represents apparently the young condition only, as 

 above described. 



GENUS II. ZYGOSELMIS, Dujardin. 



Animalcules highly metabolical and variable in form, swimming with 

 the aid of two unequally developed flagellate appendages, which issue from 

 the pointed anterior extremity ; oral aperture at the base of these flagella, 

 followed by a distinct tubular pharynx ; endoplasm transparent, granular ; 

 no eye-like pigment-specks. Inhabiting fresh water. 



In their constantly changing form, the animalcules of this genus may be most 

 appropriately regarded as biflagellate Astasia. Butschli has proposed to identify 

 the type species Z. nebulosum with Chilomonas paramecium, an animalcule, however, 

 with which, excepting for its possession of two flagellate appendages, it can scarcely 

 be said to share a single point in common. 



Zygoselmis nebulosa, Duj. PL. XXI. FIGS. 52 AND 53. 



Body variable, ovate, globular, or pyriform, changing its form slowly 

 from one to the other, endoplasm densely granulate ; cuticular surface 

 finely striate obliquely ; flagella of conspicuously diverse length. Length 

 of body 1-1250" to 1-500". HAB. Pond water. 



Stein records the existence of a distinct oral aperture and pharyngeal passage 

 at the base of the two flagella, and delineates an example in his recently published 

 volume, reproduced at PI. XXI. Fig. 53, whose body is abnormally distended 

 through the ingestion of two comparatively large diatom frustules. The animalcule 

 at Fig. 59, bearing three flagellate appendages, is, as explained by Stein, about to 

 divide by longitudinal fission. Dujardin, who appears to have observed this type 

 on one occasion only, describes it as incessantly changing its form as it swims through 

 the water, after the manner of an Astasia. 



Zygoselmis insequalis, Perty. 



Body hyaline, colourless, slowly assuming various shapes ; one flagellum 

 somewhat shorter than the other ; parenchyma sometimes filled with clear 

 green granules ; movements sluggish. Length 1-840". 



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