238 THE PHENOMENON OF 



with the constrictive division of the Conferva-cells, or vs'ith 

 free cell-formation, becomes softened to some extent, if 

 we reflect that the process which we have termed con- 

 striction is by no means a mere mechanical process of 

 folding-in, but rather a process of definition advancing in 

 the form of an annularly penetrating incision, that in this 

 case also the external division is preceded by the internal, 

 first expressed in the formation of two new nuclei, as 

 may be demonstrated at least in Spirogyra. Consequently 

 the question is, essentially, in which cases does the 

 cell-formation complete the development of the bounda- 

 ries on all sides and in all parts simultaneously, and in 

 which does it advance gradually and according to definite 

 laws. On this point, I am convinced, nature will be 

 found to exhibit a far greater multiformity than has 

 hitherto been suspected. As the cell in its subsequent 

 development displays sometimes an all-sided growth, 

 sometimes a one-sided, sometimes a two-sided, or a 

 growth regularly distributed in varying intensity in a 

 still more complicated way, there certainly exists a variety 

 of cases of regulated progress in the very first develop- 

 ment of the boundaries of the cell. Thus, in the lower 

 plants, there undoubtedly exists a division advancing 

 from one end of the cell to the other. In Chlamidococcus 

 pluvialis, in which the division of the cell in the later 

 active generations often begins even before the cessation 

 of the movement (see p. 208), I have very frequently 

 seen the division advance very gradually from the pos- 

 terior to the anterior, still ciliated extremity. A one- 

 sided advance of the division from the upper end of the 

 cell to the lower (which corresponds to the ciliated ex- 

 tremity of swarming gonidia) may be conjectured of 

 the Diatomacese with fan-shaped cells and dichotomous 

 peduncles {Gomphonema), as also of the Palmellacese 

 with delicate peduncles issuing from the internal cell-mass. 

 {Dictyosphcerium, Nag.) As regards the ordinary cell- 

 division, apparently taking place simultaneously over the 

 whole surface, it is a question whether or not the pri- 



