DEVELOPMENT. 137 



may be either continuous or discontinuous : the parts havino- 

 different axes may continue united, or they may separate. 

 Instances of each alternative are supplied by both plants 

 and animals. Continuous, multiaxial development, is 



that which plants usually display ; and need not be illustrated 

 further than by reference to every garden. As cases of it in 

 animals may be named, all the compound Hydrozoa and Ac- 

 tinozoa; and such molluscous forms as the Botryllidce. Of 



multiaxial development that is discontinuous, a familiar 

 instance among plants exists in the common strawberry. 

 This sends out over the neighbouring surface, long slender 

 shoots, bearing at their extremities buds that presently strike 

 roots, and become new individuals ; and these by and by lose 

 their connexions with the original axis. Other plants there 

 are that produce certain specialized buds called bulbils, which 

 separating themselves and falling to the ground, grow into 

 independent plants. Among animals the fresh-water polype 

 very clearly shows this mode of development : the young 

 polypes, budding out from its surface, severally arrange 

 their parts around distinct axes, and eventually detaching 

 themselves, lead separate lives, and produce other polypes 

 after the same fashion. By some of the lower Annulosa, this 

 multiplication of axes from an original axis, is carried on after 

 a different manner : the string of segments spontaneously 

 divides ; and after further growth, division recurs in one or 

 both of the halves. And in the Aphides, we have a still fur- 

 ther modification of this process. 



Grouping together its several modes as above delineated, 

 we see that 



r Unicentral 



Central ] or r Continuous 



( Multicentral < or 



D. j C Discontinuous 



EVELOPMENT IS < Or 



Uniaxial 



Axial ^ or C Continuous 



Multiaxial j or 



^ Discontinuous 



