258 THE PHENOMENON OF 



rupted, the two secondary nuclei vanish, and in place of 

 each one of them appear two tertiary, making four nuclei 

 in a cell, which either lie in one plane, or are arranged 

 like the angles of a tetrahedron, and the formation of the 

 four special mother-cells now takes place directly around 

 these. Supported by these observations, we might cer- 

 tainly conjecture, that all those processes of cell-formation 

 which, according to the external definition of the cells, 

 appear as direct quarterings, are essentially the same as 

 the double halving, only distinguished from the latter by 

 skipping over one step of the course of the formative 

 process, advancing, namely, from the first halving, 

 already indicated by the formation of two secondary 

 nuclei in the interior of the cell, without completing this, 

 to the succeeding halving. 



In the multiplication of the Unicellular Algse, especially 

 in the family of the Palmellacege and those nearest allied 

 to them, we meet with undoubted cases of true quartering 

 (in the sense just explained), together with apparent 

 quartering. The latter results from the first halving, 

 which produces merely a transitory generation of cells, 

 being followed immediately by a second.* Here also 

 the arrangement of the cells in one plane not unfrequently 

 alternates with the decussate, as I have observed, for 

 example, in CMamidococcus pluvialis. Nageli gives 

 genuine (and tetrahedral) quartering as the character of the 

 genus Tetrachococcus, the independence of which he, how- 

 ever, doubts himself, placing it as a sub-genus under 

 Pleurocococcus, and leaving it undecided whether the form 

 of Alga thus characterised does not belong to PI. mlgaris.\ 

 I have observed intermingled, in Protococcus viridis, mere 

 halving, apparent (decussating) and true (tetrahedral) 

 quartering ; the latter two distinguishable by the form of 

 the cells, from which alone I could draw inferences as to 

 the mode of formation in this case. 



* I h^ve already directed attentioij to the circumstauce, above,(p,160, note ) 

 t Nageli, ' Zeitschrift,' 1847, p. 70, (Ray Transl,, 1849, p. 140,) 'Neuer. 

 j\lgensyst./ p. 127. 



