OBSERVATIONS ON POLYZOA. 199 



the works of foreign naturalists. References, however, are 

 always made to the original publications, and the state- 

 ments used have been, in all cases, sifted of facts that did 

 not correspond with my own researches upon closely allied 

 American species. 



The nomenclature of Professor Allman's exhaustive 

 "Monograph of the Fresh-water Polyzoa" has been adopted 

 throughout, with the exception of a few alterations, which 

 become necessary, partly in consequence of some ideas of 

 my own, with regard to the composition of the organs, dif- 

 fering from those of Prof. Allman, and, partly, because I 

 here adopt a new view of the relations of the anterior and 

 posterior poles of the body, originated by my friend Edward 

 S. Morse.* In an article published in these Proceedings 

 he homologizes the parts of the animal in the various classes 

 of the Mollusca, and arrives at the conclusion, as surpris- 

 ing, as it is truthful, that the attached end of a Polyzoon 

 is in reality the anterior, and that the peduncular end of a 

 Brachiopod is the homologue of this, and, also, anterior. 



It therefore becomes necessary to alter the commonly re- 

 ceived nomenclature, and to denominate the attached end 

 of a Polyzoon the anterior; the free end the posterior; the 

 anal side the dorsal; and the opposite, or so called hsemal 

 side, the ventral. 



*A Classification of Mollusca based on the principle of Cephalizatiou. 

 Proc. of Essex Inst., Vol. IV, No. VI, p. 1G2. 



Note. I am indebted to Dr. Joseph Leidy, of Philadelphia, for iden- 

 tifying my specimens of Fredericella regina with his species, for tra- 

 cings of all the species described by him, and for other valuable infor- 

 mation. 1 desire, also, to return thanks to Professor H. J. Clark, of 

 Harvard College, Professor A. E. Verrill, of Yale College, Professor 

 Alfred Mayer, of Penn. University, Professor Theodore Gill, of the 

 Smithsonian Institution, Mr. Elliott Smith and Mr. S. I. Smith, of 

 Norway, Maine; to all of wliom I am under obligations for important 

 assistance. 



My thanks are also due to the Officers of the Smithsonian Institution, 

 of Washington, and the Peabody Institute, of Baltimore, for the use of 

 books which I could not have otherwise obtained. 



It is but just that I should also express the feelings of gratitude with 

 which I cherish the memory of my father, Mr. Alpheus Hyatt, of Bal- 

 timore, whose long continued generosity, while living, enabled me not 

 only to accomplish this undertaking, but to plan, and prosecute others 

 of a similar kind. 



Mr. Edward S. Morse perfected the drawings with the skill of an 



