20 



NATURAL HISTORY. 



appearance, as far as this can be done in black and white, but their colors 

 arc their greatest attraction. The figure shows the ramified, root-like 

 base, from which arise the straw-colored stalks, each supporting a red 

 hydroid, with its numerous tentacles, between which the racemes of 

 brightly colored reproductive organs hang gracefully down. 



In others of the hydroids an additional complication is introduced ; for 

 the reproductive organs, instead of producing eggs to be set free, develop 

 jelly-fishes, which finally burst from the enclosing walls, and begin a free 

 life. All of these hydroid jelly-fishes are small, but size is not a requisite 

 of beauty. For grace of outline some of these forms cannot be excelled. 



The adjacent figure (Fig. 19) will serve as 

 the type of our description. It is a com- 

 mon form on the New England coast dur- 

 ing August and September. It consists of 

 a crystalline bell, or umbrella, about three- 

 quarters of an inch in diameter, from the 

 margins of which arise a number of slender 

 tentacles. Inside the bell a proboscis hangs 

 down, bearing the mouth at its extremity. 

 The digestive tract is simple, consisting 

 merety of a central chamber, with which 

 the mouth communicates, and from which 

 eight canals radiate to the margin of the 

 bell. On these canals the reproductive 

 folds occur. Inside the margin of the bell 

 is a delicate membrane, perforated with a 

 circular opening, which considerably con- 

 tracts the aperture of the bell. In the form figured, the proboscis and the 

 reproductive organs are a pale yellow, or straw color, but in others red, 

 pink, green, and gold occur. 



It is not only in the day-time that these forms are beautiful, for by 

 night they have a charm. The naturalist knows that many forms seek 

 the lower waters by day ; but at night, when the surface of the sea is 

 smooth, they rise to the surface, and so the student at the shore goes 

 ; * skimming." He has a net made of fine, thin cloth, which he drags along 

 the surface behind a slowly moving boat, taking it up at intervals, and 

 rinsing its contents into a pail. At such times, if the night be dark, he 

 can occasionally see floating gracefully through the water one or more of 

 these jelly-fishes, their crystalline bell lighted up just enough to show its 

 outlines, by the pale phosphorescent glow which proceeds from the pro- 

 boscis. In the pail in which the captives are taken the jelly-fish are 



Fig. 19. 



■Jelly-fish of Melicertum r<i)n- 

 panula. 



