NUTRITION PROPER. 



343 



Fig. 229. — Diagram of a medusa : nn, 

 nerve; m, mouth; st, stomach; rt, 

 radiating tubes. 



take it by means of what have been called nettle cells, 

 or stinging cells, or thread cells (nematocysts), or, by 

 Agassiz, most appropri- 

 ately, lasso cells. They 

 occur in clusters, espe- 

 cially on the tentacles. 

 Their shape, like an elec- 

 tric lamp, is seen in Fig. 

 230, A. Examined with 

 the microscope, they are 

 seen to contain — like an 

 electric lamp — a fine 

 thread coiled within. If 

 the animal be irritated 

 the long thread flashes out like lightning (Fig. 230, B) 

 and its extremity pierces, discharges a poison, and par- 

 alyzes its prey, which is 

 then slowly brought to 

 the mouth and swallowed. 

 The effect of these sting- 

 ing cells, with their in- 

 visible threads charged 

 with poison, is so power- 

 ful that handling these 

 animals will produce pain- 

 ful inflammation of the 

 hands. 



The mouth is the open- 

 ing at the end of the pro- 

 boscis (Fig. 229), and the 

 stomach — often called the 

 oesophagus — the hollow 

 proboscis itself. The food 

 is taken by the mouth, and retained in the stomach until 

 digested. Whatever is indigestible is rejected through 



Fig. 230. — Lasso cell : A, in passive 

 state ; B, with the thread discharg- 

 ing. 



