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159 



perfect, but whose researches are nevertheless of great vahie, 

 conckided that the whole bud was derived from the proHfera- 

 tion of the ectoderm. Had his statement proved correct, the 

 explanation of the process of budding in the Polyzoa, based on 

 the idioplasm, would be just as simple as in the case of Hydroids : 

 it would then only have been necessary to suppose that the cell 

 in which proliferation first began contained accessory idioplasm 

 in the form of ' blastogenic idioplasm.' Seeliger was, however, 

 unable to support Nitsche's statements, and the most recent 

 observations of Oka,* Davenport,f and Braem,J prove beyond 

 doubt that the • mesoderm cells ' of the parent take part in the 

 formation of the buds. We must therefore suppose that certain 

 mesoderm cells, provided with definite groups of determinants 

 for muscles, endothelia, and sexual organs, migrate into the bud. 

 It is quite conceivable that muscles, and more especially endo- 

 thelia, should be developed in this manner, but it would be 

 difficult to understand how free cells from the body-cavity of the 

 parent could migrate into the bud, and there give rise to sexual 

 organs at perfectly definite regions : were this so, we must sup- 

 pose that in reality certain of the cells only, and not any of 

 them, are concerned in the migration. Such an assumption is, 

 however, contradicted by the abnormal processes of budding 

 which occur, for instance, in Pedicillina. I therefore do not 

 consider that the question of the origin of the sexual organs is 

 yet decided, but I suspect, nevertheless, that one or two of the 

 mesoderm cells of the bud are derived from the primary prolif- 

 eration of the ectoderm. This view is supported by Seeliger's 

 statement that he considers such a derivation of individual 

 mesoderm cells of the bud possible, at any rate, in the case of 

 Loxoso7na.% 



As, however, we are not specially concerned with the process 

 of budding in the Polyzoa in particular, but are only making 



* A. Oka, ' Observations on Freshwater Polyzoa,' Journ, of College of 

 Science, Imperial University, Japan, Vol. iv., Pt. i, 1890. 



t C. B. Davenport, ' Observations on Budding in Paludicilla and some 

 other Bryozoa," Bull, of the Museum of Comp. Zool. at Harvard College, 

 Vol. xxii.. No. I, 1891. 



t F. Braem, ' Untersuch. iiber d. Bryozoen des sussen Wassers,* Bibl. 

 Zool., Cassel, 1890. 



^S Seeliger, ' Bemerkungen zur Knospenentwicklung der Bryozoen,' 

 Zeitschr. f. wiss. Zool., Bd. 50, p. 564. 



