EVOLUTION OF PHANEROGAMS 175 



complex than previously, taking the form of a sexual 

 megazooid. So that when members of this type came to 

 develop and multiply in aerial conditions as the first 

 Angiosperms, the sexual structure took a form differing 

 greatly from that of the Gymnosperms. 



Now it has been shown on page 94 how the medusiform 

 gonophore evolved from the sporosac-gonoblastidium, as 

 the result of terminal compression during development in 

 aqueous environment, so that if we can show that the 

 Angiosperm flower has its homologies with the medusiform 

 gonophore in a convincing way, the conclusion that the 

 Angiosperms were a fresh stock derived from the sea is 

 tempting. Any resemblances they have to Gymnosperms 

 would thus not indicate terrestrial derivation from these 

 plants, but only separate derivation from two distinct kinds 

 of marine continuously zooidal type at a great interval 

 of time. 



The fact that during given past periods the same organic 

 types flourished at far distant parts of the globe, as is 

 proved by the fossils found, would seem to have a simple 

 explanation, namely, that at a given depth a world-wide 

 distribution of a marine stock would obtain in the sea during 

 long ages, and that the elevation of the ocean bed to form 

 dry land in a given period would supply at different parts 

 of the globe a common primitive stock for adaptation to 

 aerial conditions. Thus, through the subsidence of the 

 land Palaeozoic vegetation largely disappeared, and when 

 in the Mesozoic period fresh upheavals of land occurred 

 they bore with them at different parts of the globe a fresh 

 marine zooidal type which became a new form of plant-life. 



This marine type, it is suggested, possessed attached 

 medusiform gonophores, and in several primitive forms 

 became the first Angiosperms. It is unnecessary to say 

 that the origination of the Angiosperm would be due to 

 development in the new environmental conditions. 



The attached medusoids of hydrozoa known to us are 

 of considerable variety, but they are all alike in being com- 

 posed of a bell manubrium, and radiating canals (usually 

 four, six, or eight in number). The canals communicate 

 with the cavity of the manubrium, and are linked together 

 by a circular canal running round the rim of the bell. The 



