GENUS E UGLENA . 381 



improbably be to some extent homologous with it. The flagellum was in all cases 

 demonstrated to take its origin within the interior and close to the bottom of the 

 infundibuliform excavation. 



Euglena viridis, Ehr. Pl. XX. Figs, 29-51. 



Body elongate, subcylindrical or fusiform, exceedingly flexible and 

 variable in shape, mostly rounded anteriorly, and with a short, transparent, 

 conically pointed, tail-like posterior prolongation ; cuticular surface faintly 

 striate obliquely ; endoplasm usually entirely bright green, but sometimes 

 changing to dark orange or red ; flagellum slender, exceeding the body in 

 length, a red pigment-spot generally present at the anterior extremity ; 

 contractile vesicle situated at the anterior extremity, close to the coloured 

 pigment-spot ; endoplast, spherical, subcentral. Length 1-600" to 1-140". 



Hab. — Pond and stagnant water, on the surface of which it frequently 

 occurs in vast shoals. 



The aspects presented by this animalcule under various developmental or 

 external conditions are so numerous and diverse as to have led to its description by 

 the earlier writers under several specific titles. There can be little doubt that the 

 Etiglena sangiimea of Ehrenberg, having the same external form, but of a blood-red 

 colour, or variegated with red and green, represents one of the matured phases of 

 the species now under consideration, while the E. hyalina of the same authority 

 illustrates a still less well-marked variation, in which, through probably the absence 

 of suitable food-material, the endoplasm is almost completely transparent. It is 

 maintained by Perty that the Amblyophis viridis of Ehrenberg — which has received 

 a separate generic title on account merely of the rounded instead of pointed and 

 more tail-like posterior extremity — is also a variation only of Euglena viridis, it 

 occurring in company with the normal animalcules, and according to him being 

 reproduced directly from them. As the latter generic distinction is, however, allowed 

 by more recent writers, including more especially Stein, it appears desirable to retain 

 it in this treatise. 



Endogenous multiplication, manifested by the division of the entire coloured 

 inner substance of Euglena vi?idis into germs of variable number and subfusiform 

 or irregular contour, as shown at PI. XX. Figs. 36 and 37, and in a manner 

 most nearly resembling that already recorded of Polytonia 7(vella, was observed 

 by the present author in connection with the observations relating to the oral 

 apparatus previously described, as also encystment, attended sometimes by and 

 sometimes without the coalescence of two individual zooids. The result of the 

 process of encystment, as shown at PI. XX. Figs. 49 and 50, was the breaking up 

 of the entire protoplasmic body-contents into numerous globular spore-like bodies, 

 which were ultimately released as small, green, creeping amoebae. Fig. 51, pos- 

 sessing at this early stage no trace of the flagellum, oral aperture, or pigment- 

 spot which were subsequently acquired. The fusiform zooids produced by the 

 subdivision of the internal substance of the motile Euglcnce appear on the contrary 

 to be furnished in most instances with both a flagellum and eye-speck, on bursting 

 through the investing membrane of the parent cell ; this observation is further con- 

 firmed by the investigations of both Kolliker and Mr. Carter. In addition to the 

 reproductive form of encystment just described, Euglena is in the habit, upon the 

 drying up of the ponds or ditches that contain it, of assuming a spherical form and, 

 throwing around itself a gelatinous envelope which becomes gradually indurated, of 

 remaining in this quiescent state until the return of genial conditions. In this 

 manner the temporarily encysted EuglencR often form film-like expansions of con- 

 siderable extent, and have been mistaken for independent forms of Algse. Microcystis 

 oUvacca and M. Noltii, as also the Protococcus turgidus and P. chalybius of Kiitzing, 

 are thus now regarded as representing variable phases of this resting condition of 



