192 GENERAL HISTORY OF THE INFUSORIA. 



beyond the ring." In AmhlyopMs viridis the red jDigment may either entirely 

 or only partially fiU the dark areola. Perty very sensibly remarks, " All 

 these red stigmata are deficient of all the requisites of an eye — they have no 

 refracting medium ; and the presence of an eye is inconceivable among beings 

 which have neither nervous centres nor communicating nerves. They are 

 probably nothing more than drops of red-oil, like those which are produced 

 among the chlorophyll in imicellidar Algae " (p. 118). Another fact, bearing 

 on the character of a red pigment- speck in Euglence, is the change of colour 

 these beings at times undergo fi'om green to red, just as Chlamydococcus and 

 various unicellular Algae do when they enter on the " resting " stage. 



JReprodudion of Asfasicea. — In Ehrenberg's opinion, the members of this 

 family are reproduced both by self- division and by ova : he speaks of having 

 witnessed the former process in the genus Euglena, but only as a rare 

 occurrence. In other genera he failed to discover it. A\Tien fission takes 

 place it docs so in the usual manner, longitudinally, and produces two equal 

 and similar organisms ; rarely, the new beings are of unequal size. More- 

 over, in the encysted condition, which was mistaken by Ehrenberg for the 

 death of the Euglena, or confounded ^Adth other structures, fission is a con- 

 stant phenomenon. 



"WTien the motile Euglena becomes "still," or enters into a state of rest, it 

 contracts itself into a ball, and, while retaining its red stigma, loses its fila- 

 ment. A gelatinous layer is thi'own out around it, which gradually hardens 

 into a rigid colourless cyst : this at first lies close upon the mass of the Euglena, 

 but ultimately is removed from it all round by an interval ; and when quite 

 matiu'e, it frequently acquii'es a brownish colour and opacity. In the encysted 

 condition, Euglena closely resembles the "stiU" cells of Protococmis ; hence 

 the term " Protococcoid/' to express this condition. When Euglence have 

 undergone this transformation, they cohere together by a mucilaginous ex- 

 cretion, so as to form expansions or films resembling in appearance those 

 produced by many Palmellew. 



This close resemblance subsisting between encysted Euglence and the rest- 

 ing-spores of numerous Algae, e. g. of (Edogonium, explains many of the 

 wonderful transformations recounted, such as the germinating of encysted 

 Euglena-ceWs into branching filiform Algae. Again, the filmy masses pro- 

 duced by Euglenm have been described as independent genera and species of 

 Algae, — as, for instance, those formed by E. viridis, as Microcystis olivacea, 

 and those by E. sanguinea, as Microcystis Noltii. 



That the contained green Euglena is not dead within its case, is proved by 

 its sometimes being seen to revolve within it, and also by the circumstance 

 that, in the early period of encysting, on rupturing the cyst, the contained 

 being escapes and resumes the appearance and movements of its free brethi^en. 

 It would seem, indeed, that Euglena: are in the habit of temporarily encysting 

 themselves as a means of protection against injurious external causes, such as 

 evaporation, and that, when a normal condition is restored, they throw off 

 their protecting envelope and reassume their active contractile character and 

 movements. The empty cases are often to be met with floating on the sur- 

 face of water, united with others and with encysted Euglenoi in a common 

 membranous mass. The vitality of the enclosed being is further displayed 

 by the process of fission, which advances in the power of two until very small 

 segments are produced, which soon develope severally a red speck and fila- 

 ment, and, on the dissolution or rupture of the common cell-wall of the parent, 

 escape as small free-moving corpuscles rather resembhng Monads than Eu- 

 glence by their minuteness. 



The encysting act maj^ transpire in very small as well as in large Euglence, 



