2o6 THE SEAS 



by a sudden twisting movement, they drive the edge of their 

 own shell in between the open valves, which are thus held 

 apart sufficiently to allow the proboscis to be pushed in 

 (Plate 75) Others again grip the shell of their prey with 

 their broad feet and force the edges together, cracking off 

 pieces near the edge until a hole is made large enough to 

 allow the proboscis to enter. The sea slugs frequently 

 browse on stationary animals ; thus the sea lemon, Doris, 

 spends its life scraping sponge into its mouth with its broad 

 radula ; the beautifully coloured JEoMs feeds on anemones, 

 being apparently quite unharmed by the nettle cells. It is 

 a very remarkable fact that these nettle cells, after they have 

 been swallowed, are transported into the little projections on 

 the back of the ^olis, where they establish themselves and 

 in which they are always found, so that the older naturaUsts 

 thought they actually developed there. Their value to 

 the iEolis, if any, is not very clear, though they may help 

 to protect it. One little sea slug called Calma feeds 

 exclusively on the eggs and embryos of shore fishes, which 

 are laid on stones and shells. When feeding, its face fits 

 like a hood over the egg, which is slit open by the narrow, 

 saw-like radula and the contents swallowed. There is 

 another type of carnivorous marine snail, the boat-shell, 

 Scaphander, which swallows small bivalves whole and then 

 crushes them to pieces in a special gizzard lined with Umy 

 or horny plates and worked by powerful muscles. 



The active pelagic squids pursue shoals of fish near the 

 surface. The octopus and cuttlefish lie concealed, the one 

 in crevices among rocks and the other in the sand, and dart 

 out upon their prey, usually fish or crabs, which they seize 

 by means of their tentacles armed with suckers. They are 

 particularly careful when attacking crabs to seize them from 

 behind so that these are unable to defend themselves by 

 means of their claws, which are gripped firmly by the 



