THE STARFISH AND ITS ALLIES 205 



each ray, ending on the muscles of the tube feet. If this nerve ring is cut, 

 then the different rays do not act together, but one set of tube feet pull in 

 one direction and those of another ray pull in another, thus preventing 

 locomotion. At the extreme end of each ray the nerve is found to end in 

 a tiny eye spot. In your specimen it may show as a salmon-pink spot at 

 the outer end of the ambulacral groove. This eye spot probably cannot 

 distinguish form, but by means of it the starfish can distinguish between 

 light and darkness. 



Organs of Breathing. — The starfish spends most of its life in the water, 

 although it may be found attached to rocks or under moist seaweed after 

 the tide has receded. In common with all animals and plants it must have 

 oxygen. Some oxygen is taken in with the water in the system of water 

 tubes within the body, and some is taken out of the water by means of delicate 

 fingerlike processes of the skin called branchice. The branchiae protrude from 

 between the spines of the dorsal surface. They may be withdrawn by the 

 animal. They are much too delicate to withstand drying and cannot be 

 seen on the specimen you are studying. 



Food of the Starfish. — The food and method of feeding are of con- 

 siderable interest to us because of the economic value of the clams, 

 oysters, and other mollusks on which the starfish feed. Starfish are enor- 

 mously destructive of young clams and oysters, as the following evidence, 

 collected by Professor A. D. Mead of Brown University, shows. A single 

 starfish was confined in an aquarium with fifty-six young clams. The 

 largest clam was about the length of one arm of the starfish, the smallest 

 about ten millimeters in length. In six days every clam in the aquarium 

 was devoured. The method of capturing and killing their prey shows that 

 they, in some instances, appear to smother the mollusk by wrapping around 

 it with their soft baggy stomach. The latest evidence on the subject, how- 

 ever, seems to show that they wrap around the valves of the mollusk and 

 actually pull apart the valves by means of their tube feet, some of which 

 are attached to one valve and some to the other of their victim. Once the 

 soft part of the mollusk is exposed, the stomach envelops it and it is rapidly 

 digested and changed to a fluid. ^ This it can do because of the five large 

 digestive glands which occupy a large part of each ray, and which pour 

 their digestive fluids into five pouchlike extensions of the stomach extend- 

 ing into each ray. 



Damage to the amount of thousands of dollars is done annually to the 

 oysters in Connecticut alone, by the ravages of starfish. During the sum- 

 mer months the oyster boats are to be found at work raking the beds for 

 starfish, which are collected and thrown ashore by the thousands. 



' Observation by one of my pupils, F. T. Lacy, seems to show that in the case 

 of the mussel the starfish inserts part of the stomach into the hole through which 

 the byssus protrudes, and kills the mussel by means of the digestive fluid. When 

 the shells gape, the starfish finishes the meal at its leisure. 



