172 THE EVOLUTION OF CONTINUITY 



repetition of the internodes the repetition of zooidal structure 

 in the marine colony. In fact, we believe that the internode 

 is the plant " zooid," and that the plant stem or branch 

 represents a continuous series of ancestral zooids as modified 

 by aerial conditions, having been made to develop in such 

 close Continuity that separate identity has been lost and 

 internal structure completely changed. But though the 

 flowering plant is not a zooidal colony, yet each " zooid " 

 has the power of behaving in certain respects as a 

 separate unit, being able to originate another by process 

 of gemmation so that a continuous series results. This 

 alone points irresistibly to the zooidal derivation of the 

 Phanaerogam. 



But this is not all. For while we hold that the inter- 

 nodes are the terrestrial representatives of the nutritive 



Fig. 48. — Diagram of different forms of sexual structure in 

 marine zooidal colonies, a, sporosac ; 6, disguised medusoid ; 

 c, attached medusiform gonophore ; d, free-swimming medusi- 

 form gonophore. (After Nicholson.) 



and supporting zooids of Hydrozoal colonies, we further 

 suggest that the flower-structure of the former are homo- 

 logous with the fructifications of the latter in certain aspects. 

 For the marine zooidal colonies of the present time have, 

 like Phanserogams, their cones and flowers. Here it is 

 necessary to turn our attention to the reproductive organs 

 of zooidal colonies. 



On an earlier page we have noted that the reproductive 

 " zooids " (so-called) of hydrozoal colonies differ entirely 

 in appearance from the vegetative or true zooids. And the 

 reproductive structure may be comparatively simple in 

 design, or the reverse. There are four typical forms of 

 sexual apparatus met with, all these, though distinctly 



