540 



Marvels of the Universe 



redevelops into a new polj'p. The whole colony may be the growth of only a few weeks, as may be 

 proved by floating a plank or a cork buoy for a short time in the sea and finding it supporting a 

 number of such colonies. 



On many of these Hydroid colonies at certain seasons there will be found cells of urn-like shape, 

 larger than the others, containing special Hydroids. The ordinary cell contains what we may call 

 worker Hydroids, borrowing a name from the hone}' bee community. They are sexless individuals, 

 unable to propagate their species ; but the special cells contain sexual individuals. In some species 

 these remain attached to their cells and produce eggs, which float off and hatch into larvae like that 

 by which the colony was founded. In other cases — such as Obelia — they develop into minute 

 jeUy-fishes, which quit their cells and float away. They are very small — less than a quarter of an 

 inch across — and transparent. Scarcely anybody but the naturalist ever sees them, though towards 

 the end of summer the sea-water near the shore may be thick with them. A fine muslin net drawn 

 through the water and then rinsed in a vessel of sea-water will yield scores or hundreds of them. 

 In a few cases these develop into quite large jelly-fishes, such as may be noticed by the average 

 seaside visitor. These jelly-fishes produce eggs, which are distributed in the sea as they swim about 

 by pulsations of the little bell. One of our photographs (page 537) shows an enlarged representation 

 of the jelly-fish stage of Obelia, after it has floated off from the colony, and in another photograph 

 (page 535), of a different species, these jelly-fishes are seen still in their crystal vases ready to 

 depart. 



The Sickle Coralline, of which a small portion is shown under the microscope in the photograph 

 on page 538, has its stems and branches spirally twisted, giving a distinct and pretty appearance 

 to the plant-like colony. Another photograph (page 534) shows a magnified portion of one of the 

 Sea-Feathers, so called because the branches are arranged equally on each side of the stem and so 

 bring about a resemblance to a bird's feather. A number of different species of these Sea-Feathers 

 may be found upon our own coasts, and they may be readily distinguished from other groups by 



Pholo by'] 



[ir. N. II, , ri.l.j, . F./..! 



THE BOMMI FISH. 



The fish is said to prefer to lie with the extremity of its tail in water, and it is enabled in some way to oxygenate its 



blood through the tail-fin. 



