No. 644] ARRESTED EVOLUTION 



261 



cells and the mother-cell, but develops into a complex pro- 

 cess in the multicellular forms. Distinct budding occurs 

 already in the protozoans as in Arcella, where a number 

 of small buds are constricted off all round. In sponges 

 it is developed to such a degree that no one can fail to 

 recognize the impossibility of drawing any rigid line be- 

 tween growth and asexual reproduction.^ In the coelen- 

 terates asexual reproduction runs riot, as Greddes and 

 Thompson state. It is, further, by far the prevailing 

 mode of reproduction among the stoek-building br\-ozo- 

 ans; it also is common among marine worms, as with 

 the famous palolo-worm off the coast of Samoa, and fi- 

 nally it is also frequently found among the tunicates. 



The primitive character of this mode of reproduction 

 can not be doubted. It probably in all cases is an in- 

 herited character that persisted from the ancestral pro- 

 tozoans. It has by many zoologists been considered as 

 an acquired character among the tunicates, but Van 

 Name^ has lately advanced good reasons for the conclu- 

 sion that it is also a primitive character among the as- 

 cidians inherited from their remotest ancestors and that 

 it is not a faculty that can be acquired secondarily. 



Budding leads to the formation of colonies or stocks. 

 These as a rule are not favorable to a swimming or va- 

 grant mode of life, hence by far the majority of budding 

 forms are sessile, although there are a considerable num- 

 ber of exceptions in the swimming siphonophores, cteno- 

 phores, floating graptolites, and compound swimming 

 worms and ascidians. Since most of the colonial stocks 

 are sessile, budding has often been considered as having 

 been induced by a sessile mode of life and thus held to 

 be a function that could be acquired. Its absence among 

 the sessile cirripedes seems, however, to support Van 



2Geddes, Patrick, and Thompson, J. Arthur, "The Evolution of Sex," 

 London and New York, 1914, p. 205. 



3 Van Name, Willard G., "Budding in Compound Ascidians and other 

 Invertebrates, and its bearing on the Question of the Early Ancestry of 

 the Vertebrates," Bull. Amer. Mns. Nat. Hist., Vol. 44. art. 15, 1921, pp. 

 275-282. 



