SEX AND BREEDING 57 



spective of the full moon near Suez. In a later paper, however (1938, 

 IV), he agrees with Fox with regard to Diadema, but for other echino- 

 derms studied "there is not much support for a lunar periodicity," and 

 he considers lunar periodicity in the Echinoderms near Suez a rare 

 exception (p. 12). 



. There is no evidence of periodicity in Arbacia punctulata, but the lunar 

 periodicity of the worm Nereis limbata at Woods Hole is well established 

 (Lillie and Just, 191 3), also of the "fireworm" in Bermuda, of the pa- 

 lolo worm and of many other animals. A good evaluation of lunar 

 periodicity in sea urchins and other animals is given by Korringa, 1947, 

 Ecological Monographs, 17 : 349-381. 



g. Forced Shedding 



Arbacia punctulata may be induced to shed its eggs and sperm by cutting 

 the animal or injuring it in other ways. Miss Palmer (1935, 1937) dis- 

 covered that spawning may be induced by injecting tissue extract, 

 KCl, or CaClg into the perivisceral cavity through a sHt in the test. 

 I found that one has merely to inject with a pipette some KCl or NaCl 

 solutions into the mouth, through the teeth to induce shedding (E. B. 

 Harvey, 1939c). Tyler (1949 a) advocates an injection of 0.5 cc. of 

 0.5 M KCl which is practically isosmotic, into the body cavity of an 

 average sized Arbacia. The animal, after injection, is held over a dish 

 of sea water into which the eggs or sperm are shed. Although eggs may 

 be collected in this way and the animal remain uninjured, it has been 

 my experience that sometimes the eggs are not fertilizable, even after 

 repeated washings with sea water (E. B. Harvey, 1939b). This has also 

 been the experience of many other investigators, especially during the 

 summer of 1950 when the scarcity o^ Arbacia necessitated conservation 

 of the animals. It would seem that there is some substance on the out- 

 side of the shell, a dermal secretion perhaps, which is toxic to the eggs, 

 rather than the perivisceral fluid which has been often considered 

 toxic (see under Perivisceral Fluid, Part IV, especially reference to Pe- 

 quegnat, 1948). If one has a female half covered with sea water into 

 which the eggs are being shed, one finds that the shed eggs will not 

 form a fertilization membrane or be fertilized on addition of sperm, 

 whereas the eggs from inside the animal give 100% fertilization. The 

 same observations had been made previously by Ohshima (1921). 

 Professor Runnstrom, during the summer of 1950 at Woods Hole, found 

 that the toxic effect could be overcome by the addition of sodium 

 periodate (5 X 10-^ M) to the sea water (personal communication). 



