CHAPTER 7 



Sex and Breeding 



a. Sex Ratio 



To investigators working on Arbacia eggs, it always seems as though 

 there were many more males than females. An accurate count of the 

 animals shows that this is not so, but they are approximately equal in 

 number. Shapiro (1935 a) found that throughout one season the ratio 

 was I male to 1.03 females (2,358 animals). Ikeda (1931) found the 

 ratio in Temnopleurus toreumaticus was i female to 1.018 males (2,093 

 animals). 



b. Sex dimorphism (Other Species) 



No external morphological difference between the sexes has been 

 detected in Arbacia punctulata, and this is true of most sea urchins. There 

 are, however, a few species in which the males and females differ or 

 have been reported to differ in size or shape of the test, in the genital 

 pores or genital papillae, and in the color of the tube feet. 



In Arbacia lixula, Cerami (1924, as quoted by La Cascia, 1930) 

 thought that the male has a taller and rounder shell and a larger 

 peristome and lantern, but La Cascia (1930), on measuring a greater 

 number of specimens found no sex difference. 



There is some disagreement about Paracentrotus lividus. O. Schmidt 

 (1878 in Brehm's Thierleben Abt. 4, Bd. 2, Wirbellose Thiere) says that 

 his boatman, in Lesina, could tell the males and females apart from 

 the boat; the males were smaller, darker, and more spherical, the 

 females flatter and more reddish violet. He says that his boatman was 

 never deceived, but he had difficulty himself in distinguishing them. 

 Camerano (1890) found no difference in color in the two sexes, but 

 agreed with Schmidt that the males were smaller and the females 

 flatter. However, La Cascia (1930), on making a more thorough study, 

 concluded that one could not distinguish the males and females by 

 shape or size. In the Japanese form, Temnopleurus toreumaticus, Ikeda 

 (1931) found from a careful biometric study that the males are slightly 



