THE LOWER FORMS OF LIFE. 



93 



more or less rough, for phosphorescence, upon which the light depends, 

 is only produced when the creature is irritated. 



The Medusa or "jelly fish," or "sea blubber," as it is sometimes 

 called consists of a more or less hemispherical or globular mass of 

 sparkling crystal-like jelly, arranged in the form of an umbrella ; 

 and hence this part of its body is, in scientific language, called the 

 "umbrella." Underneath, however, the analogy to the umbrella is 

 somewhat lost, for, to make the resemblance complete, we should 

 carry the dilating wires of the umbrella to the edge, and cover them 

 in beneath with another piece of silk we should then form what is 

 in scientific language called the "sub-umbrella." Were the stick of 



Fig. 118. - Pelagia cyaneaa, tentacles ; 6, arms ; c, umbrella. 



the umbrella cut off a few inches below where it would enter the 

 centre of this sub-umbrella, it would represent the dependent polypite 

 of the Medusa, which again is either single or divided into what are 

 called arms, as shown in Fig. 118 and Fig. 119 (p. 94). 



But the reader must imagine further, that, where the polypite 

 depends from the sub-umbrella, there is in the Medusa a cavity in 

 the gelatinous substance, and that this cavity communicates, on the 

 one hand, with the polypite, and on the other, by means of four, six, 

 eight, ten, or more canals, called "radiating canals," with the rim 

 of the umbrella (Fig. 122, b, p. 96). Bound the rim of the umbrella is 



