2 THE HYDROIDA IN GENERAL. 



animated flowers wliich root themselves to the sea-bed, these no less wonderful Medusa^, with 

 functions higher and more varied, lead a life of freedom. They love the upper regions of the 

 sea, and wherever over its wide surface the conditions suited to their welfare are to be found 

 there will the towing-net encounter them. A thousand leagues away from land, where the shij) 

 lies motionless in the calm, there they are abroad in their unnumbered hosts ; and where the 

 gale is strong, and the wave breaks upon the rocky headland, there too they congregate and 

 sport imharmed in the surf. And yet for days together the towing-net may sweep the sea 

 without a trace of them, for they are sensitive to every changing mood of the atmosphere above 

 them ; they feel the gathering cloud and the summer shower; and when the sea freshens beneath 

 the falling rain-drops, or the air rests upon its surface with influences unfavorable to their well- 

 being, they sink into salter waters and find shelter in more genial depths. 



But their life was not always one of freedom as it now is, for they once grew as buds upon 

 those strange hydroids, which, with the life of the animal, root themselves to the sea-bed like a 

 plant; they sprung forth from their sides, and drew their nourishment from the parent branch, 

 and expanded and developed themselves until they became fitted for an independent existence, 

 and then, full of a new and higher life, they broke away from their supporting stalk, active and 

 energetic beings, unrivalled in the gracefulness of their motions and in the symmetry and beauty 

 of their forms. 



The true significance of all this budding and blossoming, of this imitation by the animal 

 of the form and growth of the plant, lies at the foundation of a scientific knowledge of the 

 Hydroida, and constitutes one of the most interesting and marvellous chapters in the 

 morphology and physiology of animals. 



It is my intention to devote the present work to an examination of the Hydroida in their 

 general morphological and physiological relations as a great natural group ; while to one large 

 and important subdivision of this group, the Tubulari/ice, a more special consideration will be 

 given, and all the genera and species of which it is composed will be described in detail. 

 Thus, a purely descriptive zoology of the Tubulariiice will be combined with a careful study of 

 their structure and physiology, and of the structure and physiology of the entire order of the 

 Hydroida, that more comprehensive group under which the T/ibularince are immediately 

 included. 



When thus investigated, it will be found that the study of the Hydroida possesses an 

 interest far beyond what we may at first be inclined to attribute to beings so simple in their 

 structure and so apparently insignificant in the place allotted to them in the economy of nature, 

 for we shall then learn that some of the most important facts in morphology and some of the 

 highest laws in physiology find in them their expression and elucidation. 



SYSTEMATIC POSITION. 



The Hydroida of the present monograph include the Hi/drin(P, TiibidarinfB, CampanularincB, 

 and Sertidari/ia, being so far exactly coextensive with the Hydroida of Johnston.' The group 

 Hydroida, however, as here understood, necessarily embraces most of the so-called naked-eyed 

 or gymnophthalinic Medusae, for a large proportion of these are known to be the free generative 



' George Johnston, ' A History of the British Zoophytes.' Second Edition, 1847. 



