94 THE EVOLUTION OF CONTINUITY 



Thus, the compression of the developing sporosac- 

 gonoblastidium fused what should have otherwise become 

 successive sporosacs, in lateral Continuity around a shortened 

 and widened central stem whose hollow interior com- 

 municated at the base with a varying number of radiating 

 tubes, each representing the central spade of a sporosac. 

 Between these tubes or canals the sporosac walls developed 

 in lateral continuity, and thus would be formed the bell 

 or umbrella of the medusiform gonophore, whose nourish- 

 ment finally called for the formation round the bell-rim of 



Fig. 29. — The evolution of the medusiform gonophore. a, 

 sporosac -gonoblastidium ; B, the theoretical results of com- 

 pression during development of a, the results being incom- 

 plete ; o, the perfect plan of the medusiform gonophore, 

 a further development of b. b is diagrammatic of what is 

 known as a " disguised medusoid." 



a circular canal from the ends of the radiating canals 

 (Fig. 29). 



There is still a higher form of sexual structure met with 

 in Hydrozoal colonies, in the form of a gonoblastidium 

 containing medusiform gonophores — a further intensification 

 of Continuity, or of terminal compression. Its chief interest 

 is in connection with terrestrial plant-evolution which is 

 dealt with in a later chapter. It may be mentioned here, 

 however, that in Phanserogams (Flowering Plants and Trees) 

 we see a transition from zooidal to megazooidal Conti- 

 nuity parallel to that just described. In both cases the 

 phenomenon is directly connected with the function of 

 reproduction, and, as has already been said, we can 



