HYATT, OBSERVATIONS ON POLYZOA. 197 



XIII. Observations on Poly zoa. Suborder Phylactolcemata. 

 By ALPHEUS HYATT. 



With nine Plates. 



[Communicated October 10,* 1864.] 

 INTRODUCTION. 



The investigations recorded in the following pages are 

 the results of observations made on the American species 

 of the Phylactolsemata ; with the intention of elucidating 

 the structure of the genera, and of presenting the laws of 

 their structural combination as fully as this can be ac- 

 complished within the limits of the present communication. 



For this purpose synoptical tables have been given, ex- 

 hibiting the anatomy of the different divisions, as far as 

 our knowledge of ihe adult animals would permit. 



Had such a plan been possible at the present time, the 

 synopsis would have embraced only the anatomy of the 

 most complicated species of each generic series; and other 

 tables, similarly constructed, illustrating every genus, would 

 have been prefixed, one individual of each species being 

 selected for analysis. But the small number of species 

 now known in each genus not affording material enough 

 for perfecting this system, the tables include only general 

 statements of the characters of each genus, and these are 

 arranged in a linear series in order to show clearly their 

 serial relations. I venture, however, to assert, that, not- 

 withstanding these defects, the results obtained by this 

 mode of procedure are more exact, than if the usual me- 

 thods of describing the anatomy had been followed. 



The advantages of thus analyzing the anatomical fea- 

 tures of any natural division are at once apparent. Their 

 organization, as a whole, is rendered plain ; and the reader 

 is enabled to trace, throughout the structure of the group, 

 not only the changes of any organ by itself, but even of 



*During the proof reading I have embodied in the original text many 

 new facts discovered since the 10th of Oct., 1864, and the communica- 

 tion, therefore, may be considered as covering a period extending from 

 that date to the day of publication. 



ESSEX INST. PROCEED. VOL. iv. z. March, 1866. 



