INTRODUCTION, 



A GENERAL sketch of the structure of the Hydroida, and 

 the history of their reproduction and development, is a fit- 

 ting prelude to the study of our British species. It would 

 be impossible, in a systematic work like the present, to dis- 

 cuss at length the many interesting and difficult questions 

 that meet the student in this province of zoology. It will 

 rather be my aim to convey an accurate idea of the form 

 of structure that characterizes this group of animals, and 

 of the striking facts of the Hydroid life-history. 



As a preliminary, it will be necessary to define the de- 

 scriptive terms employed in this work. 



TERMINOLOGY. 



I have endeavoured to simplify in this department as 

 much as is consistent with precision, believing that a cum- 

 brous and difficult terminology is the bane of science. As 

 uniformity of practice is clearly desirable, and much con- 

 fusion arises from the use of terms in different senses, I 

 have made only those changes that seemed to be absolutely 

 necessary, and have adopted the terms that have obtained 

 most currency in the higher literature of the subject. 



A precise terminology is no doubt of great value ; but 



a 



