ON BUDDING IN ANIMALS. 19 



In taking a general survey, therefore, of budding in animals, 

 it is apparent that it reaches a high degree of frequency in 

 certain lower groups characterized by a more plastic nature — 

 for example, the Protozoa, the Sponges, the Coelenterates, the 

 Polyzoa, and compound Ascidians and the Salpidce ; while it 

 occurs less frequently in the Cestode Worms, in the lower Tur- 

 bellarians, in the bristled Annelids, and in the simple Ascidians. 

 Moreover, it is apparent that its place is taken by partheno- 

 genesis in such groups as the Crustaceans, Insects, and Piotifers. 

 It comes therefore to be a question whether any common feature 

 in regard to this mode of increase links together all the divergent 

 groups just indicated, and whether any basis exists for making 

 reliable deductions as to its origin. 



So far as can at present be ascertained, comparatively few 

 zoologists have touched on these questions. Weismann, it is 

 true, tracing the division of labour and greater and greater com- 

 plexity of organization, observes : — " Hence the single group 

 would come to be divided into two groups of cells, which may be 

 called somatic and reproductive. . . . Amongst the lowest Meta- 

 zoa, such as polyps, the capacity for reproduction still exists to 

 such a degree in the somatic cells that a small number of them 

 are able to give rise to a new organism — in fact, new individuals 

 are normally produced by means of so-called buds." The same 

 author assumes that the entire absence of development by means 

 of eggs "is to be primarily explained as an adaptation, and that 

 the alternation between sexual and asexual multiplication met 

 with in Hydromedusse, Cestodes, and others has arisen from the 

 demands made by the conditions of life — demands similar to 

 those which have determined the alternations between mono- 

 sexual and bisexual generation found in Insects, Crustaceans, 

 and others. In both classes ordinary reproduction has been 

 restricted to certain generations because it was not necessary in 

 all of them, and because such restriction was a great advantage. 

 The means by which this limitation is exercised are different in 

 the two classes, not by any means because parthenogenesis could 

 not have been introduced among the lower Metazoa, but because 

 nature did not require it, but resorted to the far more practicable 

 and flexible methods of fission and budding."* 



* Weismann, ii. p. 221. 



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