160 



MORPHOLOGICAL DEVELOPMENT. 



higher Algce, exemplified in Figs. 32, 34, 35, show this very 



clearly. Here the departure from 

 the simple cell-form to the form of 

 an elongated prism, is manifestly 

 ^subordinated to the contrasts in the 

 relations of the parts. And it is 

 interesting to observe how, in one 

 of the branches of Fig. 32, we pass 

 from the small, almost-spherical 

 cells which terminate the branch- 

 lets, to the large, much-modified 

 cells which, join the main stem, 



through gradations obviously related in their changed 



forms to the altered actions their positions expose them to. 

 More simply, but quite as conclusively, do the inferior 



Algce, of which Figs. 19 — 23 are examples, show us how 



cells pass from their original spherical symmetry into radial 

 symmetry, as they pass from a state in which they are simi- 

 larly-conditioned on all sides, to a state in which two of their 

 opposite sides or ends are conditioned in ways that are like 

 one another, but unlike the ways in which all other sides are 

 conditioned. 



Still more instructive are the morphological differentiations 

 of those protophytes in which the first steps towards a higher 

 degree of integration are shown. Fig. 9 represents one of 

 the transitional forms of Desmidiacece. In it we see that the 

 two imier halves by which the individuals are united, differ 



