THE C(ELENTERATE8 



133 



from their progenitor, and so the growth proceeds until an 

 extensive colony of hundreds of individuals has been formed. 



We have spoken of the hydroid 

 communities as being washed up on 

 the beaches of our rocky coasts, but 

 the collector of these interesting objects 

 should not depend on such specimens 

 for purposes of study. It is undoubt- 

 edly true that splendid examples of 

 the sea firs and their allies are fre- 

 quently washed up by the waves, 

 including some species that inhabit 

 deep water, and which are, conse- 

 quently, not to be found by the ordi- 

 nary collector in their proper habitat, 

 and that these may often be secured 

 with the polypites still alive ; but 

 several species are to be obtained 

 between the tide-marks, especially at 

 extreme low water, growing on rocks, 

 weeds, and shells ; and we have often 

 met with good specimens, still alive, 

 attached to the shells of whelks, 

 scallops, &c., in fishmongers' stores, 

 even in inland towns. 



Sometimes individual polypites 

 become detached from a colony, and 

 develop into little umbrella-shaped 

 jelly-fishes, about a fifth of an inch in 

 diameter ; and these float about freely, 

 keeping themselves near the surface 

 by rhythmic contractions of their 

 ' bells,' the margins of which are 

 fringed by numerous fine tentacles. 

 The mouth is situated centrally on 

 the under side, and is surrounded by 

 a circular canal from which proceed 

 radiating tubes ; and pigmented spots, 

 supposed to be rudimentary eyes, are 

 formed round the edge. These little Fm> S4 ._ Antennulwia 

 bodies are called Medusoids, and may antennia 



