PULLULATION IN THE GENETIC CYCLE. 1 .") 1 



the plienomenon bj tlie term pullidation, in allusion to the 

 sprouting of leaf-shoots in a tree, which is, in fact, merely 

 a special case of a process of this kind. But the expression 

 is here employed simply to denote a continuous succession ( »f 

 gemmse in the same phase of development, ^vithout restriction 

 to cases in which they remain in this state of adhesion to each 

 other. No such distinction, indeed, could be well carried out ; 

 for gemmse ordinarily attached sometimes become separate, 

 so as to originate distinct organisms ; and variations in this 

 respect are met with not only in comparing allied species, 

 but even in the same species under altered circumstances. 



On the whole, however, such a general rule as this seems 

 to prevail — that in the Vegetable Kingdom, and in the 

 lower divisions of the Animal Kingdom, whose diffuse vita- 

 lity favours such development, the outgro\\i:hs do, witli 

 some exceptions, remain in adhesion to form compound organ- 

 isms, while from the incompatibility of such structures with 

 the more concentrated vitality of the higher animals, such 

 pullulation is either wholly excluded, as in Vertebrata, or, 

 as in Articulata — where it manifests itself exceptionally 

 — the gemmse are detached as soon as matured, and 

 assume the guise of independent animals. Such an excep- 

 tional case is that of the Aphides among insects, already 

 referred to. However great the prima facie diversity be- 

 tween the successive swarms of free insects which we here 

 meet with, and the clustered buds of the plant or the zoo- 

 phyte, the physiological identity of their relations has been 

 well demonstrated by Owen, Carpenter, and otliers, who 

 clearly show that the only difference lies in a character, the 

 variable and accidental nature of which has just been no- 

 ticed — viz., the bond of connection between the gemmje, 

 whose presence in the form of a common axis associates in 

 organic union the successive puUulations of the plant or 

 zoophyte, and whose disappearance in the Aphides disso- 

 ciates the derivative zooids, as the snapping of the tliread 



