MONOGBAPH OF THE EXISTING CRINOIDS. 369 



SEXUAL DIFFERENTIATION. 



As in the other echinodenns, differentiation of the sexes is very rare in the 

 crinoids, where it only occurs in those species in which the larvae undergo their 

 development within a brooding cavity or marsupiiun. 



In Notoo^iiius virilis (figs. 1349-1352, pi. 55) the genital organs lie almost 

 entirely upon the arms, and the sexes are readily distinguished by an examination 

 of their ventral surface. In the males the enormous testes, which look like small 

 white beans, form two alternating closely appressed rows along the arms, while 

 in the females the ovaries, which are about half the size of the testes, are similarly 

 situated but are only half as large and are not in contact in the median line; the 

 marsupia when fully developed cover the entire distal side of the ovary. 



In Thaumatometra nufriv (figs. 1232-1237, pi. 38), as in Notocnnus virilis, 

 there appears to be no sexual differentiation in the calcareous structures. The 

 females are readily distinguished from the males, however, by the marsupia, which 

 occur in the form of deep pocket-like grooves on either side indifferently of the 

 genital pinnules. 



In Isomefra vivipara (figs. 1238-1240, pi. 38) the genital pinnules of the 

 females have the third and fourth segments enormously expanded distally and 

 the fifth slightlj' expanded, serving as a protection for the ovaries and the mar- 

 supium. The genital pinnules of the males and of the immature females have the 

 third-sixth segments slightly and symmetrically expanded. 



Besides these three comatulids, only 5 or 6 other echinoderms exhibit sexual 

 dimorphism. 



In one or two of the spatangoids the lateral petals of the female are much 

 broader and deeper than those of the male and serve as brood chambers, and in 

 Anochanus there is a highly developed brood pouch. 



One of the clypeastroids has the female with the abactinal area deeply 

 depressed to form a horseshoe-shaped brood chamber, which is not found in the 

 male. 



In one of the holothurians the female has a peculiar brood chamber developed 

 in the dorsal integument. 



In one of the ophiurans the male has five arms, while the female has from 

 six to eight. 



None of the asteroids are known to exhibit sexual dimorphism. 



All of the sexually dimorphic echinoderms are from the antarctic or sub- 

 antarctic seas except Anochamis, which was described from China. 



SPAWNING SEASON. 



COMATELLA XIGRA. 



A specimen of this species taken near Jolo (Sulu), Philippine Islands, on 

 February 14, 1908, has the eggs apparently ready for extrusion. 



COMISSIA SPANOSCHISTUM. 



According to Dr. H. L. Clark, specimens of this species with the genital 

 pinnules immensely swollen with the reproductive cells were taken in March and 

 A]iril, 1914, by the Australian fisheries steamer Endenvour. 



