SURFACE-SWIMMING FAUNA (INVERTEBRATES). 99 



stages in the life-history of one species. When 

 the anatomy of a Chain-salp is minutely examined 

 it is found to contain a single egg, which gives rise 

 to a young Salp similar in nearly all details to the 

 solitary one. This escapes from its parent's body 

 when it is old enough to take care of itself, and 

 leads an independent existence. After it has 

 grown to its full size it gives rise to a stalk 

 which divides up into a number of young Salps, 

 attached to one another in a 

 very characteristic manner. 



Here, then, we have another 



instance of alternation of 



generations similar in this 



respect to the example pre- 



; viously quoted among the 



Jelly-fish, in that the one 



generation produces an egg, 



and the other numerous buds ; 



but differing from it in the fact 



i that in the case of the Salps 



both generations are adapted 



for freely swimming at the 



\ surface of the sea. 



Space does not allow us to say more in detail 



about the other animals of the Plankton that 



! belong to the same group as the Salps ; of the 



wonderfully interesting life-history of Doliolum ; 



\ of the extraordinary bright light emitted by 



Pyros&rw, or of the remarkable little Fritillaria, 



shaped like a tad-pole, living in its house of jelly. 



The story of each of these might take a whole 



chapter to itself and still be only partly told. 



Anyone who is acquainted with the general 



FIG. 27. Solitary 

 form of Salp, bear- 

 ing a young stalk 

 of Chain-salps. 



