C<ELEXTERATES. 



25 



jelly-fish, which by growth gradually becomes like the parent form. 



Here the effect of the alternation is to form many jelly-fishes from one 



egg. The young of the blue-jelly here figured 

 was taken but a short time after it had left the 

 pile of saucers, and yet had begun to grow the 

 long tentacles so characteristic of the adult form. 

 Closely allied to these two forms is a third 

 one, which differs markedly in that it never 

 swims freely. It is a small form, readily over- 

 looked by the casual observer, and which conse- 

 quently has received 

 no common name. 

 Lucernaria is what 

 the naturalist calls it. 

 One species is com- 

 mon on our north- 

 ern shores. It has 

 a quadrangular body 

 supported on a stout 

 stalk, and is colored 

 green, like the sea- 

 weed on which it 

 occurs most abun- 

 dantly. 

 The tubular jelly-fishes, the Siphonophores 



of naturalists, contain many beautiful forms, 



which, however, are far more abundant in 



tropical waters than in colder climes. The 



whole life of most of the species is spent 



in a free condition, and they are even more 



abundant on the high seas than near land. In 



our figure is represented a form occurring 



in Massachusetts Bay. At the top is a small 



float (/), while below it come a number of 



swimming-bells (n), each with much the same 



structure as the hvdroicl iellv-fish described Fig. 26.--Tubuiar jelly- 



J j j $is cara). 



above. These, however, have nothing to do 



except to force the whole colony along. From the float a long axis 

 extends downward, bearing besides the swimming-bells a large number 

 of organs: some for feeding (p), some for reproduction, while others are 

 protective (b). At intervals long tentacles (t) spring out, curling in every 



Fig. 25. — A young blue-jelly (Cy- 

 ■'in a) soon after escaping from 

 the pile of saucers. 



