HYDROZOA. 83 



the entire fabric continues to attach itself And, 

 since gemmation may take place in many different 

 ways, so, in like manner, result the great variety 

 of forms due to modifications of what is essentially 

 the same process of growth. In the flower-like 

 Tuhularia indivisa, the coenosarc consists of 

 several simple tubes, intertwined one with another 

 near their attached extremities, and sometimes 

 rising to a height of ten or twelve inches {fig. i6). 

 From the distal ends of these tubes, which are of 

 a straw-yellow colour, the polypites, tinged with a 

 bright scarlet, conspicuously project. The hydro- 

 soma of EudendriuTn rameum, though seldom 

 mors than six inches in height, bears a singularly 

 close resemblance to a forest-tree in miniature, its 

 surface being studded with minute reddish poly- 

 pites, not less than a thousand of which may 

 crowd the branches of a single specimen. Such 

 arborescent structures strikingly contrast with the 

 slender mossy threads which compose the con- 

 necting stem of smaller species. In Hydradinia, 

 the meshes of the very intricate creeping coenosarc 

 are aggregated so as to form a compact lamina or 

 crust, investing the surfaces of univalve shells, 

 which, by a coincidence hitherto unexplained, 

 usually afford shelter to the Hermit-Crab. The 

 living coating of Hydractinia presents to the 

 naked eye the appearance of a rather coarse floc- 

 culent nap, pale grey or milk-white in tint, the 

 polypites, when fully expanded, attaining a height 

 of nearly half an inch, and waving to and fro 

 with every agitation of the shell {Jig. 17, c.) In 

 other genera the colour of the coenosarc is usually 

 yellowish-brown. All the preceding forms have 

 the hydrosoma rooted, or attached to other objects^ 



G 2 



