120 THE SEAS 



rounding its mouth, are a number of powerful hook-like 

 teeth, and with these it can seize on its prey, which it 

 rapidly devours. Often it can be seen to have within its 

 stomach one or two of the copepod Calanus, and, when very 

 young herring are abundant, it will capture them and eat 

 them even though they be as long as itself. 



Another very beautiful plankton worm is the Tomopteris, 

 which has a row of wing-like feet down either side of its body, 

 with which it paddles its way through the water with a 

 curious wriggling motion (Fig. 25). 



In warm ocean waters there are commonly to be found 

 numbers of animals known as Salps. These are closely allied 

 to the common sea squirts, which lead a sedentary existence 

 fixed to rocks and piers ; but unlike its relative, the Salp 

 lives a free drifting existence in the open waters. It is an 

 inch or more in length, shaped like a barrel, and perfectly 

 transparent. They are not usually to be seen in northern 

 waters, and when found are a fairly reliable indication of 

 the presence of Gulf Stream water. 



Belonging to the same group of animals is the Pyrosoma, 

 so remarkable for its phosphorescence. The Pyrosoma 

 suffers a curious indignity at the hands of a small crusta- 

 cean, the Phronima, a glass-like creature, all head and 

 eyes. The Phronima eats off all the living portion of 

 the Pyrosoma (which is really a colony of animals) and 

 then retires inside the barrel-like skin that is left (Fig. 26). 

 This interesting beast is sometimes to be seen within its 

 gelatinous home, surrounded by a brood of young, and has 

 been observed to navigate its home about in the water. 



But the members of the plankton are too numerous to 

 mention here. The best book is nature itself, and therefore 

 at the irst opportunity one should make a small tow-net, 

 take a small boat and row out about a mile from the shore 

 on a calm day, drop the net overboard until it is a few feet 



