REJUVENESCENCE IN NATURE. 293 



cell becomes broken geniculately, though only at a very 

 obtuse angle. The opening produced by the slight 

 dehiscence of the outer cell-membrane, forming a cross- 

 slit in one side, is immediately occupied by two thickened 

 projections of an internal cell-membrane issuing out. 

 These two thickened processes are the ends of two deli- 

 cate-walled daughter-cells, meeting in the centre of the 

 mother- cell, and which are probably formed by division 

 of the contents of the mother-cell very shortly before the 

 beginning of the conjugation. Since only these internal 

 cells enter into the conjugation, we have here, not, as 

 appears at first, a simple conjugation of two cells, but, 

 strictly speaking, a conjugation of ttvo pairs of cells; 

 since, moreover, the two issuing processes, which unite 

 with the two coming to meet them from the other side, 

 are the ends of the two internal cells, Closterium lineatum 

 affords the rare example of a copulatio apicalis. The 

 individuals destined to conjugation lying near together, 

 the thickened projections do not grow out into long 

 processes, but apply themselves, in the form of everted 

 lips, directly upon the corresponding parts of the other 

 individual, or, if this has not yet pushed out its thickened 

 processes, upon its closed external cell-wall. This pro- 

 cess of the commencement of conjugation cannot be 

 described better than by comparing it to the contact of 

 four thickened firmly appressed lips in a kiss mouth to 

 mouth. The thickened projections are originally trans- 

 parent and almost colourless, since only a few green 

 granules can be observed in them, often in distinctly circu- 

 lating motion, entering at the back and retiring from the 

 front into the interior of the cell ; the green contents 

 soon follow, however, in abundant quantity. The four 

 protuberances next become so densely filled with green 

 matter and pressed so closely together, that the coupling 

 growth and anastomosis taking place during this crowding 

 up cannot readily be traced, but it is clearly shown by 

 the result. Sometimes the delicate membrane of the 

 protuberance bursts under the pressure of the contents, 



