114 GENEEAL HISTORY OF THE IIs^FUSORIA. 



fined, and, as it were, surrounded by a delicate transparent membrane." 

 The green colour is due to chlorophyll vesicles and granules, either diffused 

 or collected in a layer just beneath the surface. Among other contents are 

 also starch-granules without colour, and very frequently globules of oil. 



Green or red may exist alone : but more frequently green prevails ; and the 

 red pigment, sometimes termed erythrin or erytliropliyU, is seen only at one 

 spot, occasionally at the centre, but usually on one side of it, or at one ex- 

 tremity: when occupying the position last-named, it was looked upon by 

 Ehrenberg as an eye-speck or organ of vision. 



Although, as Cohn (op. cit. U.S. p. 528) tells us, the green and red coloui'- 

 ing matters differ in chemical and physical conditions, yet the one passes into 

 the other. The red or bro^vnish-red colour is formed when the cells become 

 drier ; but neither deficiency of water nor the influence of light appears to be 

 the exclusive cause of the transition. It is especially in the transition to red 

 that vesicles of an oUy aspect make their appearance. Indeed, that oil is really 

 formed, is supported both by analogy yviih the spores of many Algae which 

 clearly secrete that substance, and by the vesicles in question having a similar 

 refraction to oil, and behaving like it \\'ith alcohol and ether. " The forma- 

 tion of fixed oil," says Braun {Rejuv., R. S. p. 200), " is intimately connected 

 Tvith that of starch in the economy of ceU-Hfe ; its appearance, in like manner, 

 announces the repose of age in cell-hfe ; its disappearance, the beginning of 

 rejuvenescence. We meet with fixed oil in the cells, either mixed with starch, 

 substituted for it, or gradually displacing it ; its occiuTcnce is perhaps still 

 more general than that of starch .... Like the latter, it is met with in greatest 

 abimdance in those parts in which vegetation is destined to rest and to await 

 a future re-awakening ;" and such are the resting-cells of Phytozoa, in which 

 a red colom- predominates or exists alone. Braun furnishes an illustration of 

 this in his remarks on Clilamydomonas duiing its sleeping or resting state 

 (op. cit. p. 214). The opinion, moreover, that the so-called redeye-specks of 

 Phytozoa are no other than drops of oil, is shared by Perty (j). 117) and by 

 Nageli (Emzell. AJg. p. 9). 



Speaking of Protococciis, Cohn remarks (op. cit. p. o26), " The red and the 

 green portions of the contents appear to be of equal physiological importance 

 .... AMien still or motile cells are brought into contact with a veiy weak 

 watery solution of iodine, they become internally, in most parts, of an intense 

 violet or blue colour." Yet he does not believe this coloui' to depend, in 

 all instances, upon starch ; for the red contents are equally coloured blue, and 

 he therefore sui'mises there may be some other substance besides starch ex- 

 hibiting the same reaction vidth iodine. 



Besides diffused chlorophyll -particles, to which the green coloiu'is due, one, 

 two, three, or more large nuclear-hke vesicles exist in Phytozoa — indeed, in 

 unicellular plants generally — described by Xageli under the name of ' clihro- 

 phyJl utricles or vesicles.^ The number of such in any genus seems commonly 

 to be constant : thus, in StejphanosplicBra there are two ; in Gonium only one. 

 However, they are occasionally absent, chiefly so m more minute examples. 

 In Protococcus (Chlamydococcus), Cohn says they occur piincipaUy in the green 

 cells, to the number of one, two, three or more, having the appearance of 

 minute green rings, about 0-002'" in diameter — the interior being sometimes 

 darker, at others more clear, and frequently almost opake. Niigeli regarded 

 them as minute membranous vesicles, containing a mucus coloured by chloro- 

 phyll. Cohn imagined that in Protococcus they stood in connexion with the 

 division of the cell, but could not determine with certainty that their number 

 corresponded with that of the secondary cells. Kiitzing looked upon them 

 as gonidia or cell-nuclei, concerned in the propagation of the individual. 



