1912.] The Locomotor Function of the Lantern in Echinus. 101 



retraction and swing into new position, accompanied by partial opening of 

 the teeth. In (2) the weight of the urchin will not be sufficient to supply- 

 counter resistance. Even out of water the weight alone could only cause the 

 teeth to make slight marks on a frond of Laminaria (p. 91). Under water 

 there must be strong fixation by the sucker feet, and the need for fixation 

 will be all the greater when the urchin is grazing on a vertical surface. As a 

 matter of fact, urchins travelling out of water over the prepared plasticene 

 surfaces often took a small bite out of the plasticene at each step. The 

 boluses, however, were not properly taken up into the gullet, but tended to 

 remain within the grasp of the lower ends of the teeth. 



The screwing action of the lantern referred to on p. 95 will obviously 

 be of use in biting into hard or tough surfaces as well as in separating 

 weeds, barnacles, worm tubes, etc, from the surfaces to which they are 

 attached. 



Boring. — In the Clyde area, Echinus esculent us and Echinus miliaris are not 

 recognised as having a boring habit, though F. Caillaud* ascribes such a habit 

 to the latter on the coasts of Brittany. 



The same author states that Strongylocentrotus 1 /cuius and Echinus miliaris 

 excavate cavities by a knocking or striking action of the teeth. P. Fischerf- 

 agrees in general with Caillaud, while M. Hesse* also records Echinus miliaris 

 as having a boring habit. G. John§ gives a full description of the cavities 

 made by different urchins in the lava recks of San Miguel, and believes 

 that these cavities are formed chiefly by the action of the teeth, though 

 the spines also play a part, probably by giving the urchin a rotary 

 movement. 



If into the knocking action of the teeth spoken of by Caillaud we read just 

 such movements as I have shown to occur in locomotion, viz. : protrusion of 

 the teeth in the open condition, followed by still further protrusion with 

 powerful closure and a sidelong push, we shall get an action which, in course 

 of time, may well excavate cavities in rocks of moderate hardness. The teeth 

 will play the chief part, as is natural considering the extreme hardness of 

 their tips and the manner in which their length can be maintained by growth 

 from the permanent tooth germs. It is noteworthy that certain urchins with 



* " Observations sur les oursins perforants de Bretagne," ' Kev. et Mag. de Zool.,' 1856, 

 ser. 2, vol. 8, pp. 158, 179 ; " Supplement a des precedentes observations," ' Conipt. Eend.,' 

 1857, vol. 45, pp. 474—476. 



t "Note sur les perforations de l'Echinus lividus Lamk.," 'Ann. Sc. Nat.,' 1864, ser. 5 ; 

 Zool., vol. 1, pp. 321—332. 



t " Note sur les motifs que determinent les oursins a, se creuser dans les rochers des 

 reduits dans lesquels ils se logent," 1 Ann. Sc. Nat.,' 1867, ser. 5, Zool., vol. 7, pp. 257 — 263. 



§ "TJeber bohrende Seeigel," 1 Arch. f. Naturgesch.,' 1889, vol. 55, pp. 268—302. 



