MOVEMENT OF INVERTEBRATES 1l>5 



along, leaving behind it a glairy deposit which can often be 

 seen on the windows of greenhouses. Slugs move in somewhat 

 the same way, and will travel at the rate of a mile in eight 

 days, whereas the ordinary snail takes almost twice as long to 

 cover the same distance. But the slugs have another nu-tliod 

 of progression, for they have muscular waves or contractions 

 passing along the foot backwards at the rate of thirty to 

 fifty a minute. Many fresh-water snails glide in the same way 

 over the surface of water plants, and sometimes on the under 

 side of the surface-film of the water. Some of these fresh-water 

 molluscs have a curious habit of throwing out strands of 

 mucus which act like a rope up which they can climb. Simihir 

 strands of mucus, which harden into threads, are emitted by 

 certain slugs which descend quickly from plants to the ground 

 and return up the same rope. Cuttlefish have a peculiar means 

 of movement. By contracting a part of their body called the 

 mantle, they squirt out a quantity of water which ])ropels 

 them backward, for a cuttlefish generally moves with its 

 hinder end first. 



The starfish and sea-urchin movebymeans of their tube-feet, 

 "fingers," which, when they stretch them out, adhere to the sub- 

 stratum; then they contract and thus pull the body after them. 



And if "you" doubt the tale I tell, 

 Steer through the South Pacific swell ; 

 Go where the branching coral hives 

 Unending strife of endless lives, 

 Where, leagued about the 'wildered boat, 

 The rainbow jellies fill and float; 

 And, lilting where the laver^ lingers, 

 The starfish trips on all her fingers; 

 Where, 'neath his myriad spines ashock, 

 The sea-egg ripples down the rock ; 

 An orange wonder daily guessed, 

 From darkness where the cuttles rest, 

 Moored o'er the darker deeps that hide 

 The blind white sea-snake and his bride 

 Who, drowsing, nose the long-lost ships 

 Let down through darkness to their lips. 



KlPLlNO, Many Invmtions. 



The sea-urchin also helps itself along by means of its five 



calcareous teeth. 



^ Lavcr: an edible sea- weed. 



