160 SECRETS OF EARTH AND SEA 



look like stiff, motionless " teeth/' although they are 

 really, all the time, lashing and beating in regular rhythm. 

 When the animal is fixed by its tail, the lashing of the 

 cilia on the wheels causes currents in the water which set 

 with great strength to the mouth and bring floating food 

 particles to it. It is thus that the Rotifer feeds. When 

 the tail is not grasping a support, the movement of the 

 cilia on the wheels causes the animal to swim forward 

 through the water, so that it has two modes of locomotion 

 — the leech-like crawling method and the free swimming 

 method. 



The various internal organs of a Rotifer are readily seen 

 through its transparent skin (Fig. 34, A). It has a nervous 

 system, many bands of contractile muscles and a pair of 

 little tubular kidneys or nephridia, besides reproductive 

 germs (the eggs). I have here sketched only the digestive 

 canal. The mouth leads through a gullet to a very curious 

 organ called the " gizzard," marked G. All the wheel 

 animalcules have this gizzard, but its teeth, shown as two 

 oval bodies in the drawing, differ a great deal in shape 

 and complexity in the different kinds. Whilst the Rotifer 

 is feeding by bringing currents of water to its mouth, the 

 two halves of the gizzard are kept in rapid movement by 

 muscles, causing them to rub against one another and to 

 grind up the food particles which reach them through the 

 gullet. The gizzard (G) is followed by the digestive 

 stomach (St), and that by the intestine (Int), which opens 

 at the vent (V). The side (or three-quarter profile) view 

 of a similar specimen (Fig. 34, B) shows only the surface 

 of the little animal, and is intended to show especially the 

 snout-like head-lobe (S), with its two eye-spots, which 

 are red in colour. Standing out backwards from this is 

 a finger-like process (T), which is called the spur, or 

 tentacle. It has hairs at its tip, and is a sensory 



