450 THE ZOOLOGIST. 



above the anus) might serve to confuse an enemy as to whence 

 the rolling pellets came. Fishes and Starfishes seem to be the 

 chief enemies of Sea-Urchins.* Defence by disguise may be 

 effective against fishes, but it would probably be of little use 

 against the Starfishes, which find their food by scent. When a 

 sluggish or dying Sea-Urchin is attacked by Asterina gibbosa, as 

 sometimes happens in the aquarium, t the asteroid "sits" over 

 the anus or mouth of the echinoid, and then slowly digests and 

 breaks a way through the anus, or the membrane surrounding 

 the mouth. J Two or three stones or other objects might there- 

 fore be of service to the Sea-Urchin in preventing the Starfish 



* The following are some of the published observations as to the enemies 

 of Sea-Urchins. Byrner Jones (' The Aquarian Naturalist,' 1858, p. 203) 

 states that small Echini form part of the food of the Common Starfish. 

 Ludwig (in Bronn's ' Thier-Beichs,' Echinodermen, Buch iv. 1904, p. 1302) 

 mentions that remains of Echinus have been found in the Haddock, 

 E. miliaris in the Grey Gurnard and Plaice. According to Todd (" Notes 

 on the Invertebrate Fauna and Fish-food of the Bays between the Start 

 and Exmouth," ' Jour. Mar. Biol. Assoc.,' vol. vi. N. S., 1900-3, p. 558) 

 remains of Echinus have been found in the Dab. Eichelbaum (" Uber 

 Nahrung und Ernahrungsorgane von Echinodermen," ' Wissensch. Meere- 

 sunters. Kiel, N. F.,' Bd. 11, 1910, pp. 190-200) found remains of Sea-Urchins 

 in various species of Starfishes. Schiemenz (" How do Starfishes open 

 Oysters?," translation by Allen in ' Jour. Mar. Biol. Assoc.,' vol. iv. N. S., 

 1895-7, p. 26S) saw a moderately large Sea-Urchin attacked by two indivi- 

 duals of Asterias glacialis in the aquarium at Naples. Franz (" Ueber die 

 Ernahrungsweise einiger Nordseefischer besonders der Scholle," 'Wiss. 

 Meeres. Helgoland, N. F.,' vol. ix. 1910, pp. 201 and 202) found pieces of 

 Sea-Urchins in the Wolf-fish, and Gadus minutus, &c. 



f This was the case with the individual of 39 mm. when it was dying, 

 and also with an individual (not belonging to the eleven) of 26 mm. 



I I have not seen the larger Starfishes attacking a Sea-Urchin, but it is 

 possible they would sit over the same parts. Schiemenz (loc. cit.) speaks 

 of the clever way in which the two Starfishes at Naples forced their 

 stomachs through openings which appeared little adapted for the purpose ; 

 one threw its stomach into the narrow space between spines, and the other 

 attacked the mouth, of the Sea-Urchin. Before my observations on the 

 Sea-Urchins were begun, I had found by experiments that if an Asterias 

 rubens was given a dead fish, in whose abdomen a small opening had 

 been made with the point of a knife, the asteroid would pass its stomach 

 through the opening and search the interior of tbe fish. The asteroid would 

 also pass its stomach through a puncture made in the abdomen of a dead 

 Hermit-Crab. 



