NATURAL HISTORY 43 



appeared from Whitstable after an exceptionally cold winter of 1928- 

 1929; it had been abundant there (Yonge, 1949, p. 278). 



Temporary migrations have been reported for Echinus esculentus at 

 Millport (Elmhirst, 1922; Stott, 1931). An inshore migration during 

 the spawning season has been noted and a seaward movement caused 

 by frosts and heavy weather. It has been suggested that migrations are 

 due to food conditions (Gemmill, 1900). See also Deutler (1926, p. 193). 

 Nothing is known about any migrations of Arbacia. 



There seems no doubt that the abundance of sea urchins, the locali- 

 ties in which they are found and the general condition of the animals 

 vary from year to year; this applies especially to Arbacia punctulata. 



e. Phototaxis and Light Reaction 



Arbacia punctulata move away from the light and go to a shaded or 

 darker region, by the combined action of spines and tube feet; certain 

 individuals, however, go to the light (S.J. Holmes, 191 2). Removal of 

 the so-called eyes on the ocular plates does not change the reaction. 

 Strong light on the tube feet causes them to be withdrawn. Many other 

 experiments are described by Holmes. 



The very young animals are often found in empty bivalve shells, 

 probably to get away from the light. The smallest one yet brought in 

 by the collectors at Woods Hole (diameter 6 mm. with spines) was 

 found in an empty Venus shell. When taken out it was observed always 

 to move to a shaded area, often under the empty shell, sometimes at 

 the rate of i cm. in 5 minutes (E. B. H.). 



Other species, Arbacia lixula, Sphaerechinus granularis, Centres tephanus 

 longispinus, and Paracentrotus lividus, have also been found to move away 

 from the light and seek the dark (von Uexkiill, 1896; Mangold, 1909) ; 

 and also Psammechinus miliaris (Bolin, 1926; Lindahl and Runnstrom, 

 1929). However Romanes (1885) says that "the Echini manifest a 

 strong disposition to crawl toward and remain in the light" (p. 319). 



Reactions to changes in light intensity have been studied in A. lixula, 

 Centrostephanus longispinus and Lytechinus variegatus, especially with regard 

 to the spines and pedicellariae, by von Uexkiill (1896, 1899, 1900, 1909), 

 Mangold (1909), and Cowles (191 1), and more recently Diadema antil- 

 larum has been studied by Millot (1950, 1954, Phil. Trans. Roy. Soc. 

 London B238: 187-220). 



The habit of "decorating" or "masking" themselves with bits of shell 

 and seaweed, characteristic of certain littoral species of sea urchin, has 

 been attributed by some observers to protection against light (H. L. 



