116 THE EVOLUTION OF CONTINUITY 



As regards reproductive organs, the worm has a pair 

 of ovaries in the thirteenth segment, and two pairs of testes 

 in the tenth and eleventh segments. 



Now our view of the earthworm is that its body has 

 not been divided into segments, but built up into segments, 

 and that these represent ancestral megazooids which under 

 modifying force were caused to develop in close continuity ; 

 sacrificing separate identity in order to form a single seg- 

 mental organism with nothing colonial in its structure. 

 This is in the first place confirmed by the obvious repetition 

 of the segmental unit, and, on the whole, of its contained 

 parts. It is not suggested that ancestral megazooids 

 gradually acquired the habit of growing closer and closer 

 together, but that with a suddenness quite as dramatic as 

 that suggested in the origination of the primitive sea- 

 anemone, the primitive ancestor of the earthworm appeared. 

 For the process must have been a sudden modification of 

 development ; and what we imagine is that a fertilised 

 ovum, whose development under normal environmental 

 conditions would have produced a series of medusiform 

 megazooids, was made in past ages to develop under new 

 conditions which inevitably modified the expected mature 

 plan. That true megazooidal repetition potential in the 

 fertilised ovum was modified in its attempts at realisation 

 by forces making for closer continuity. 



" But," it may be objected, " allowing that on one uniform 

 principle we may explain the evolution of the Filamentous, 

 the Discontinuously and Continuously Zooidal, and the 

 corresponding Megazooidal Individual types, is there any- 

 thing to support the supposition that a serially-medusoid 

 ancestor for the annelid ever existed ? " Undoubtedly 

 there is. It is reasonable to believe that we have a present- 

 day descendant or offshoot of such an ancestor in the inter- 

 esting Aurelia (page 103). 



At a certain stage of its development the hydra-tube 

 ■* (Fig. 34) is just a continuous series of developing medusoids. 

 It is true that as they ripen they are shed distally, one by 

 one, to live independent existences ; but before this happens 

 the " strobila " may be said to have the rough plan of a 

 segmental organism. For the alimentary tract is one tube 



