SEX AND BREEDING 55 



at certain periods, especially in September (R. D. Allen, personal 

 communication, Jan. 1955). It has been stated by Orton (1920) that 

 in parts of the sea where conditions such as temperature do not change 

 much, marine animals will breed continuously. This would apply to 

 the tropics. He bases his conclusion on the statement of Semper (1881, 

 p. 136) in Animal Life that in the PhiHppines he "could not detect a 

 single species of which he could not at all seasons find fully grown 

 specimens, young ones and freshly deposited eggs." Mortensen (1921, 

 p. 245; 1938, p. 12), however, has found this not to be true of several 

 species in the tropics which had no ripe eggs when he examined them, 

 e.g., Diadema antillarum and Echinometra vanbrunti. He thinks it likely 

 that some species in the tropics have more than one breeding season. 



O. Koehler (19 16, p. 258) made a special study o{ Paracentrotus lividus 

 at Naples, examining a group of 20 animals every five days for two 

 months (November, February), and found no regular variation in size 

 or content of the gonads. He had an ingenious method of cutting a 

 window in the test to obtain a piece of gonad, then sealing it over with 

 wax, using the same gonad for successive observations (p. 127). He 

 found that during the summer in aquaria at Naples it took one and a 

 half to two months to form ripe genital products (p. 257). Fox (1924 a), 

 however, using Koehler's window technique, found that at Roscoff 

 during the summer (water temperature 17-19 °C.), Paracentrotus lividus 

 which just after spawning contained no ripe eggs, gave ripe eggs in 

 abundance after nine days. In the one form, Diadema at Suez, that 

 has been shown to have a lunar periodicity (see below), it must take 

 about four weeks (temperature of sea water 26-29 °C.) to form new 

 genital products (Fox 1924b). Monroy (personal communication) 

 finds that at Naples the sea urchins usually shed after a storm or the 

 scirocco, and it takes a week before one can obtain new eggs. Jacques 

 Loeb (1915 a) observed that at Pacific Grove, CaHfornia, >S^ro;2^j/oc^«- 

 trotus purpuratus in a certain region (temperature 12-15 °C.) shed their 

 eggs and sperm one day in March, and immature eggs began to appear 

 during the next week and ripe eggs in about ten days. Similarly Ten- 

 nent (1910) observed that Lytechinus variegatus at Beaufort, N. C. 

 again had ripe eggs a week after he had found them empty. Tyler ( 1 949) 

 obtains new batches of eggs from Lytechinus and Strongylocentrotus of the 

 west coast at two week intervals after forced shedding, during the 

 breeding seasons. Whether the eggs obtained two weeks after forced 

 shedding in Arbacia at Woods Hole are from a regenerated ovary as 

 Tyler thinks, or are the eggs left from an incomplete previous shedding, 

 it is difficult to say, though this could be determined by Koehler's 



