178 THE EVOLUTION OF CONTINUITY 



zooids in continuous series have in aerial environment 

 developed as a straight stem, whose buds and leaves alone 

 remain to indicate what has happened ; while, as regards 

 sexual structure, parts necessary for life in watery environ- 

 ment have disappeared, or been altered in aerial environ- 

 ment, but the original plan has remained intact. 



To repeat. In watery environment, from the single 



Mm 



C' 



/rtV T ' v "* 1 t t 



shtiis iMf 



^Z7 V o a 





O' 



° o 



? F«N6. 



7 Seeo-rutits. 



r Calam'ihs 



' ^SmVOflilTTrii 





% fa^iisb, 



ittns. 



Ai»>J<"o»J»irmS. 



Fig. 53. — Suggested scheme of plant evolution. 



sporosac came the sporosac " raceme " or gonoblastidium ; 

 from this evolved the medusiform gonophore ; and finally, 

 from this last, the gonoblastidium containing many medusoid 

 gonophores. The four primitive Hydrozoal types distin- 

 guished by the mentioned forms of sexual structure appeared 

 in the sea at long intervals of time, we may believe ; and 

 each one, it seems almost certain, stocked the land at long 



