11 INTRODUCTION. 



curved and delicately tinted, which form the most varied 

 and attractive combinations. But whatever the diversity 

 of external aspect, the internal structure is conformed to 

 one very definite type. 



Before proceeding to sketch the general plan of orga- 

 nization amongst the Polyzoa, and the various zooidal 

 forms, it will be necessary to define the principal descrip- 

 tive terms employed. 



TERMINOLOGY. 



Happily this is comparatively simple, and presents no 

 special difficulty in limine to the student. A few terms, 

 which are most of them in general use, are sufficient for 

 all the purposes of accurate scientific description. 



ZOARIUM (=polyzoarium auctt.). The composite struc- 

 ture formed by repeated gemmation. 



ZOOICIUM ( cell auctt.; cystid, Nitsche; Brutkapsel, 

 Reichert). The chamber in which the polypide is lodged. 



POLYPIDE ( =polype of older authors ; bryozoid, Reich- 

 ert). The zooid, consisting of alimentary canal, with 

 tentacles, nervous ganglion, &c., which is developed within 

 the zooecium. 



C(EN<ECIUM (poiypidom, Johnston; polypary auctt.). 

 The common dermal system of a colony. 



ECTOCYST ( = ectoderm}. The outer layer of the coenoe- 

 cium. 



ENDOCYST ( = endoderm) . The inner layer of the ccenoe- 

 cium. 



ENDOSARC ( = " colonial nervous 'system/' F. Miiller; 



