P E E F A C E, 



The present work contains the result of many years' study of the remarkable 

 group of animals to whose elucidation it is devoted, a group in the investigation of 

 which ready access to the sea has afforded me special facilities. 



My object has been to work out as exhaustively as possible the general natural 

 history of the Htdroida, and besides this to give a complete descriptive Zoology of the 

 Gymnoblastic or Tubularian forms of this Order. 



The work is thus divided into two parts — the first devoted to the Morphology, 

 Physiology, Distribution, and other general considerations bearing on the entire Order 

 of the Htduoida ; the second, to descriptions of all the known genera and species 

 which compose one of its most important and interesting Sub-orders — that of the 

 Gymnohlastea. 



A very large proportion of the observations here recorded are entirely original, 

 while it has, moreover, been my aim, in giving an account of the observations of 

 others, to take nothing for granted which it was possible for me to subject to personal 

 verification. It will be seen that the amount of labour thus involved is far from 

 slight. Indeed, it is only by constant and widely extended explorations of the coast, 

 both within the tidal zone and in the deeper sea regions, followed up by laborious 

 microscopic investigations, that results of any value are to be expected. 



The plates have all been drawn from nature by myself, and are from the living 

 animal. The soft parts, which constitute the chief interest in these wonderful organ- 

 isms, are thus represented as they show themselves while the animal is still beneath the 

 waters of its native seas. This is all the more important in animals which, like the 

 gymnoblastic hydroids, retain in their dried state not a single character of value, and 

 which even in specimens preserved in spirits lose almost all their beauty and many of 

 their important zoological characters. The figures of the species, too, are all coloured 

 from life, so that not only will a more adequate idea of the beauty of these creatures 



