636 



SCIENCE PROGRESS 



trace a very striking series through Pandorina, Endorina, and 

 Pleodorina to that marvel of colonial perfection, the genus 

 Volvox (Klein 41). This series affords a very striking example 

 of the recapitulation of phylogeny by ontogeny in the invariable 

 recurrence of the flat Gonium-stage in the early phases of the 

 development of the spherical colonies and in the antheridial 

 colonies of Eudorina and Volvox, but this is only one of the 

 innumerable interesting points that a study of this series brings 

 to light. That a form very much like Chlamydomonas was the 



Fig. 2. 



A, Spondylomortan quatcrnariian, Ehrb. B, Gonium perforate, Mull. c, Chlorodendron subsalsum 

 (small portion of a colony). D, Tetraspora (with pseudocilia). B, Apiocystis Brauniana, Nag. 

 (pseudocilia). F, Physecytium confervicola, Borzi. G, Ccelastrmu proboscideum, Bohlin (single cell). 

 H, Chlorella conglomerate/. (Artari), Oltmanns. K, Scenedesunis aaitus, Meyen. L, j". acutus (spherical 

 cells formed in presence of much oxygen). M, Ccclastrum microporuvi, Nag. N, Dictyosphteriuvt 

 pukhellum, Wood. P, Schrdderia setigera, Lemm. (a and B after Stein; c after Davis; D, E and 

 p after Chodat ; f after Borzi ; g, m, n after Senn ; h after Oltmanns ; k, l after Beyerinck) 



ancestor of the group is obvious when the complete accord in 

 cell-structure between this genus and the different members 

 of the Volvocacese is recognised ; an isolated cell from a colony 

 of one of the latter is in some cases almost indistinguishable 

 from a Ch!ainydomojias-'md'iv'idua.\. As one advances along the 

 series a tendency towards division of labour among the cells 

 of the colony becomes more and more manifest. Already in 

 Pandorina (Pringsheim 57) we find that the cells at that end 

 of the colony which is directed forwards during motion have 



