28 THE AMERICAN ARBACIA 



The Arbacia punctulata collected by me in 1942 at Beaufort, N. C. 

 are considerably larger than those at Woods Hole, averaging 5 cm. 

 in diameter (without spines) and 3 cm, in height; their spines are 

 more slender and longer, measuring up to 3.5 cm. The eggs of the 

 Beaufort form are also larger, 80 tx in diameter as against 74 [x for the 

 the Woods Hole form. Jackson (1927) thinks that "the Florida material 

 differs enough from the Woods Hole type so that it might well be 

 considered a distinct local form" (p. 449). 



b. Color 



The color of Arbacia punctulata is quite variable, from reddish gray to 

 reddish to purplish to brownish to almost black. Young individuals are 

 inclined to be lighter. There is no change in color when kept in the 

 light or dark for short periods, as shown by Parker ( 1 93 1 ) for a period 

 of 10 hours. I have confirmed this several times, and Kleinholz (un- 

 pub.) has also found this. But they are affected by light if kept for 

 longer periods. A group of six animals of medium coloration which I 

 kept in the dark room at Woods Hole (in 1948) were decidedly lighter 

 than a similar group kept in bright light in a laboratory room after 

 a period of two months; there was a slight difference even after a 

 week. I have carried out similar long-time experiments for several 

 summers. Dark animals kept in the dark become darker (black) ; dark 

 animals kept in the Hght become lighter (brownish). Light animals 

 kept in the dark become greyish; light animals kept in the light be- 

 come reddish or purplish. The results are complicated by the fact that 

 there are at least two different kinds of pigment in the test and spines, 

 a melanoid and an echinochrome, and that the test and spines are 

 different in color. For pigments in A. lixula and P. lividus see Glaser 

 and Lederer (1939). 



Another experiment was carried out (summer of 1954), using the 

 same animals for light and dark exposure. A group of six Arbacia of 

 different sizes were kept in an aquarium in a very bright room with 

 sunlight (in the mornings) for a month, and kodachrome pictures were 

 then taken. This same group was then kept in a dark room under 

 exactly similar conditions (not fed), and completely shielded from any 

 light, for a month. Kodachrome pictures were taken on the same film 

 with exactly the same conditions of lighting, exposure, etc. When 

 exposed to the light the animals were decidedly more red, and there 

 was also more black pigment. 



Ultraviolet light causes the animals to become reddish (E. B. H. 



