4.8 THE AMERICAN ARBACIA 



taller than the females; but this has been denied by Mortensen (1943, 

 M. Ill, 2 p. 79 footnote). 



In Cidaris membranipora (nutrix), according to Studer (1880 b) the 

 shell of the female is flatter, while in Hemiaster (Abatus) cavernosus, the 

 shell of the male is flatter. In Goniocidaris canaliculata there is no differ- 

 ence in external form, but there is a difference in the genital plates. The 

 brood-pouches of these and several other forms also indicate the sex 

 (Studer, 1880 a) (Fig. 8). 



In some forms, genital papillae are sometimes found at the opening 

 of the genital ducts (see Bronn's Thier-Reich, 1904, Bd. II, Abt. 3, 

 Buch IV, p. II 35), and are sometimes different in the two sexes. In 

 Echinocardium mediterraneum the genital papilla of the female is thicker 

 and shorter than that of the male (Hamann, 1887 and Plate XVIII, 

 no. 7). In Echinocyamus pusillus it is much longer in the male, while in 

 Psammechinus miliaris it is present in the male, often with red pigment, 

 and is lacking in the female (Marx, 1929; see Grasse, vol. 1 1, p. 160). 

 In this species, the difference between the males and females is suf- 

 ficient for the sexes to be separated into different aquaria, as is done 

 in Runnstrom's laboratory in Kristineberg, though sometimes there 

 is a mistake and the female tank becomes clouded with sperm (personal 

 communication) . 



M. M. Swann recently (1954) has found a sHght difference in the 

 sexes in Echinus esculentus, Paracentrotus lividus, Psammechinus microtuber- 

 culatus, Ps. miliaris, and Sphaerechinus granulans. "In the male the five 

 genital pores are borne on short papillae... their edges are glistening 

 white... In the female the genital apertures are not borne on papiUae 

 but are more or less sunk below the level of the surroundings... They 

 are usually somewhat smaller than in the male and often oval in shape. 

 The glistening white edges characteristic of the male papillae are never 

 visible... The descriptions given do not apply to Arbacia lixula. Here 

 the genital apertures are sunk in circular pits, and papillae may be 

 present or absent in either sex." 



In Lytechinus anamesus and L. pictus, the gonopores of the female are 

 larger than those of the male (Tyler, 1944 and verified by C. B. Metz 



in 1953)- 



A rather striking sex dimorphism has been found by Motomura 

 (194 1 a) in the Japanese species, Strongylocentrotus pulcherrimus ; the tube 

 feet on the oral side are yellow in the female and white in the male. 



