176 THE SCIENCE OF LIFE. 



The ordinary Jelly-fish (Medusa, or Acalepli] is soft, 

 gelatinous, and bell-shaped, with tubes radiating from 



center to circumfer- 

 ence, where they con- 

 nect with a circular 

 canal. The margin is 

 fringed with stinging 

 tentacles. The radi- 

 ating parts are in mul- 

 tiples of four. These 

 gelatinous bells, vary- 

 ing from the size of a 

 pea to a foot or more 

 in diameter, float, 



FIG. 76. Development of Snrsia. i. Polyps de- 

 scribed as Syncoryne, natural size. 2. A polyp, mOUth downward, ill 

 magniried. a. Polyp stem. b. c. d. e. Medusoid n . 

 buds, in various stages. /. Tentacles of the polyp, the SCa, and propel 



themselves by flap- 

 ping their sides. (Fig. 76.) There are two representa- 

 tive forms of Medusae, the Lucernaria, or Umbrella-aca- 

 leph, attached by a short pedicle, and having tentacles 

 disposed in eight groups around the margin, and not less 

 than eight radiating canals ; and Discophora, the ordi- 

 nary Jelly-fish, free and oceanic, with four radiating 

 canals in the disk, which ramify and open into a circular 

 canal around the mouth of the disk. 



Order 2. Siphonophora, or floating Hydroids, (siphon, 

 a curved tube, and phero, to bear,) are free swimming or 

 compound floating Hydroids, with an unbranched, or 

 slightly branched, but muscular ccenosarc. The com- 

 mon stem of these colonies swims by means of enlarged 

 and altered polyphites, whose stomachs are undeveloped 



