268 MICROSCOPIC FORMS OF VEGETABLE LIFE. 



endochrome from the primordial utricle (Fig. 72, a, b). Accord- 

 ing to Mr. S. G. Osborne, however, by using the " Rainey mode- 

 rator" (§ 74), with direct sunlight and an achromatic condenser, 

 and by increasing the power to about 500 diameters (Mr. Eoss's 

 objective of l-6th in., with a deep eye-piece, being the combina- 

 tion employed), a very distinct action of cilia may be discerned, 

 both along the inner edge of the primordial utricle, between this 

 membrane and the endochrome, and along its outer edge, be- 

 neath the cellulose coat ; the action being in opposite directions 

 in these two situations, and producing two opposite currents. 

 By careful focussing, the circulation may be seen in broad streams 

 over the whole surface of the endochrome ; and these streams 

 detach and carry with them, from time to time, little oval or 

 globular bodies (a, 6), which arc put forth from it, and wliich are 

 carried by the course of the flow to the chambers at the extremi- 

 ties, where they join a crowd of similar bodies (b). In each of 

 these chambers, a current may be seen from the somewhat abrupt 

 termination of the endochrome, towards the obtuse end of the 

 cell (as indicated by the interior arrows); and the globules it 

 contains are kept in a sort of twisting movement by the action 

 of the cilia on the inner side of the primordial utricle, which can 

 here be distinctly seen as at a. Other currents are seen externally 

 to it, which seem to be kept up by the outer set of cilia ; these 

 form three or four distinct courses of globules, passing towards 

 and away from o (as indicated by the outer arrows), whei'e they 

 seem to encounter a fluid jetted towards them through an aper- 

 ture in the pi-imordial utricle at the apex of the chamber ; and 

 here some communication between the inner and the outer cur- 

 rents takes place. A corresponding aperture seems also to exist 

 in the outer cellulose coat ; for if the endochrome be forced by 

 pressure into closer proximity than usual to the obtuse termina- 

 tion of the cell, the current from its extremity may be seen to 

 spread into the surrounding fluid. This circulation is by no 

 means peculiar to Closterium ; having been seen by Mr. Osborne 

 in many other Desmidiaceae, in several of which he has also de- 

 tected what he believes to be clliar}^ action.' 



165. When the single cell has come to its full maturity, it 

 commonly multiplies itself by duplicative subdivision; but the 

 plan on which this takes place is often peculiarly modified, in 

 order to maintain the symmetry characteristic of the tribe. In 

 a cell of the simple cylindrical form of those of Bidymoprium 

 (Fig. 77), little more is necessary than the separation of the two 

 halves, and the formation of a partition between them by the 

 infolding of the primordial utricle, according to the plan already 



' See Mr. S. G. Osborne's communications to tlie " Quarterly Journal of Microscopical 

 Science," vol. ii, p. 234, and vol. iii, p. 54. Although the Circulation is an unquestion- 

 able fact, it may be doubted whether the appearance of Ciliary action is not an optical 

 illusion, due to the play of the peculiar light employed, among the moving particles of 

 the fluid. See Mr. Wenham's paper on the Circulation in the Leaf-Cells oil Anar.haris, 

 in the same Journal, vol. iii, p. 278. 



