vin 



ECHINODEBMATA— GENITAL ORGANS 



497 



the axial sinus, etc. with it downwards ; i.e., it is impossible to decide which organ 

 took the lead in shifting. (2) As the gonads which bud from the ring-like strand 

 open into the bursa, which latter, however, open outward orally, it is to some 

 extent explicable why the ring- 

 like strand descends interradi- ^* 



ally to the bursoe. 



The whole problem is still 

 further complicated by the ques- 

 tions : (1) "What was the original 

 function of the bursie ? (2) Is 

 the ventral position of the bursse 

 the primitive position ? (3) Is 

 the opening of the gonads into 

 the bursse a recent specialisation 

 in the Ophiuroidea ? 



portion 

 strand 



The curved-in 

 of the ring - like 

 (with the sinus enclosing 

 it) runs along that side of 

 each bursa which is turned 

 to the interradius. It, 

 however, gives off a branch to the wall which is turned towards 

 the radius (of the arm), this branch running along this wall from 

 its periphery to its proximal part. Both walls of the bursa, therefore, 



Fig. 3aj.— Transverse section through the disc of an 

 Ophiurid (Ophioglypha) at the base of an arm (after 

 Ludwig). 1, Dorsal wall of the disc ; 2, bulging of the 

 digestive sac ; 3, bursa ; 4, gonad on the bursal wall ; 5, base 

 of the arm ; 6, ventral wall of the disc ; 7, bursal aperture ; 

 8, genital plate ; 9, bursal scale. 



Fic. 893.— Section through an ovary of an Ophiurid (Ophioglypha lacertosa) (afterCu&ot). 

 1, Muscle trunk, cut through transversely ; 2, nerve ring ; 3, bursal wall ; 4, aperture of the ovary 

 into the bursa ; 5, wall of the genital sinus ; 6, genital sinus ; 7, the endothelium of the genital 

 sinus, which covers the gonadial wall ; 8, cavity of the gonad ; 9, eggs in a more mature condition 

 than the rest ; 10, ring-lilce strand in the aboral ring sinus (11). 



the abradial wall, i.e. that turned to the interradius, and the adradial 

 wall, i.e. that turned to the arm, have a genital strand. The abradial 

 genital strand of each bursa is merely a part of the apical ring 

 strand, while the adradial is a lateral branch of that strand. These 

 VOL. II 2 k 



