136 MARINE INVERTEBRATES 



these saucers is finally detached, and when liberated is called an 

 ephyrula, and becomes a jellyfish. Thus its cycle of life is com- 

 plete. There are some species which, having no hydroid or strobila 

 state, mature without alternation of generation (metagenesis). 



The term of life of the jellyfish does not exceed one year. 

 Even the giant Cyanea attains its immense growth in six months. 

 It starts in the spring as an ephvrula, not more than one half of 

 an inch in diameter, and when it dies in the autumn is often six 

 to eight feet in diameter. The bodies of jellyfishes are ninety- 

 nine per cent, water, and the dead ones thrown upon the beaches 

 by the autumn storms rapidly disappear, leaving no traces behind. 



The powerful stinging-cells with which the large medusae are 

 armed make them formidable enemies, and it is probable that 

 some deaths by drowning are caused by swimmers encountering 

 them and becoming paralyzed by them. 



ORDER STAUROMEDUS.E 



C" Cross-medusce ") 



GENUS Lucernaria 



L. auricula* This little iridescent jellyfish, which measures about 

 one and a half inches in diameter, is commonly found attached to eel- 

 grass by a stalk-like projection of the top of the umbrella. Short, globe- 

 tipped tentacles are arranged in eight clusters, each cluster on a raised 

 prolongation of the margin of the umbrella, and in the center of each 

 space between them is a dark kidney-shaped organ called the anchor. 

 These anchors are used for holding, either for suspension or when moving 

 from place to place. The mouth forms a slight quadrangular projection 

 in the center of the bell-like expansion. The arm-like projections are mot- 

 tled with two rows of spots, which are the ova. Although a free form 

 and capable of moving about, Lucernaria is sedentary in habit. It is 

 sometimes found free, but generally attached by its extremity to eel- 

 grass or Fucus, seldom to rocks. It is constantly changing its shape. 

 The one it most frequently assumes is that of a cup or inverted bell. It 

 is found on the New England coast. (Plate XLIV.) 



ORDER PEROMEDUSJE 



("Maimed medusce") 



GENUS Pericolpa 



P. quadrigata. Umbrella conical and divided by a horizontal con- 

 striction into two parts, the lower one being again divided into lobes. 

 There are four long tentacles and four tentaculocysts. It is not found 

 on the coasts of the United States, 



