dS! ZOOGENESIS ®l| 



This divergence, however, is not haphazard, but 

 on the contrary runs in certain very definite lines 

 resulting in the production of a series of animal types 

 each of which bears a definite relation to all the rest 

 (figs. B, C, E, pp. X40, 146, and 2.54). 



The key to this relationship is furnished by four 

 curious groups of forms having a symmetry which is 

 partly radial and partly bilateral (fig. E, p. 2.54). 



These four groups are made up of: 



I. Types which by continuous budding produce a 

 linear colony; 



-L. Types in which the budding takes place inter- 

 nally within the original unit; 



3 . Types which are solitary, each individual repre- 

 senting a single dissociated coelenterate unit; and 



4. Types which are colonial, though the indi- 

 viduals are independent of each other. 



Between each two of these types there is another 

 type which combines the characters of both, but 

 shows no trace of radial symmetry. 



Thus between the types which by continuous bud- 

 ding produce a linear colony and the types in which 

 the budding takes place internally we find a type 

 which is segmented externally and also possesses 

 internal (coelomic) budding. Between the types in 

 which the budding takes place internally within the 

 original unit and the types which are solitary, each 

 representing a single dissociated coelenterate unit, we 

 find a type which is solitary with internal budding 

 but no segmentation, and so on. 



On the basis of their fundamental characters all of 



[^95] 



