THE STARFISH AND CLOSELY RELATED ANIMALS . 143 
victim until the shell opens and the contents can be 
sucked out. 
Nutrition. Outside the stomach, throughout' the 
cavities in the rays there is a glandular mass, the liver, 
which secretes a digestive fluid and pours it into the. 
stomach. Here the food is digested and the nutriment 
absorbed. There is a very short intestine opening 
opposite the mouth. It is so small in diameter that 
the waste of the food cannot pass through it, and must 
therefore be ejected through the mouth. 
Respiration. For the most part breathing takes 
place at all parts of the body, but there are folds of the 
skin over the aboral surface which are supposed to act 
somewhat like gills. 
Reproduction. The reproductive organs, of which 
there are two in each ray, lie on the floor of the ray; 
their ducts opening in the angles between the rays. 
These openings are called the genital openings. After 
the eggs of the female and the sperms of the male 
have been discharged into the water, the eggs are fer¬ 
tilized by the sperms. From these fertilized eggs de¬ 
velop young starfish, which are at first bilateral, and 
bear no resemblance to their parents. 
Discovery. The only specialized sense-organs are 
the eye-spots at the ends of the rays. The -nervous 
system consists of a nerve around the mouth with a 
branch extending into each ray and ending in the eye- 
spot just mentioned. The sense of feeling is apparently 
dull, and the starfish seems to suffer no hardship by 
the deprivation of one or two of its rays, which quickly 
grow again when once broken off. 
Movements. The starfish and its relatives have a 
method of locomotion very different from other animals. 
Along the oral surface of the rays are the cylindrical 
tube-feet, or ambulacral feet, bearing suckers at their 
extremities. These tubes extend through the skeleton 
into the body-cavity, where they enlarge into bulbs 
called ampulla. Each bulb connects by a small tube 
