LOCOMOTION IN YOUNG PECTINATELLA. 249 



fall masses of Pcctinatella magnified already referred to. The 

 only theory of their origin, on record up to this time, is that of 

 Hyatt ('65), who believed that each mass was derived from as 

 many statoblasts as there are colonies. In the light of this study, 

 it is evident that each mass arises from relatively few, instead of 

 innumerable statoblasts, and that it is formed in a similar way to 

 the mass resulting from the two colonies, A and B, that is, 

 through the combined phenomena of growth, division and 

 locomotion. 



BROWN UNIVERSITY, 



ANATOMICAL LABORATORY, June, 1906. 



LITERATURE CITED. 

 Leidy, J. 



'51 Proceedings of the Academy of Natural Science of Philadelphia, Vol. V. 



Hyatt, A. 



'65 Observations on Polyzoa. Proc. of Essex Institute, Vol. IV. 



Allman, G. J. 



'65 Monograph of Freshwater Polyzoa. Kay Society, London. 



Allman, G. J. 



'79 On the Structure and Development of the Phylactolrematous Polyzoa. Journ. 

 of Linnean Society, Vol. 14. 



Cuvier, G. 



'90 Observations sur la Cristatella mucedo. Bull, et Memoirs de la Societe 

 Zoologique de France. 



Wesenburg-Lund, 



'96 Biologiske Studier over Ferskvandebryozoer. Med. 4 tasl. Vid. Meddel. 

 Naturhist. Foren. Kjobenli. (5) 8 Aarg. 



Recherches biologiques sur les Bryozoaires d'eau douce. (Resume en francais) 

 Ibid. 



