DRIFTING LIFE 



121 



below the surface, and then tow it slowly along for a few 

 minutes. The catch will be sufficient reward for the trouble 

 and the sight of the delicate creatures will open one's eyes 

 to the amazing abundance and diversity of this drifting 

 life that peoples the sea in every region of the globe. 



The few animals that have so far been mentioned con- 

 stitute part of what is known as the " permanent plankton," 

 that is, they live as drifting organisms for the whole of their 

 lives. There are yet other members of the plankton which 

 have adopted this mode of life for only a short period in 

 their life -history. In the coastal regions nearly every 



Fig. 26. — Phronima in dead Pyrosoma (x 3). 



animal we find has at some time drifted freely and aim- 

 lessly about in the water layers above the bottom. The 

 young of all the smaller marine animals are, when first 

 they hatch from the egg, extremely small, and in con- 

 sequence have insufficient swimming power to cover large 

 distances, and are unable to cope with the tides and cur- 

 rents. At this stage, they rise up from the bottom, if hatched 

 there, and become members of the plankton. Here they will 

 remain for shorter or longer periods, growing and developing 

 until such time as they have assumed their adult characters 



