GENITAL ORGANS. 



In all Echini the genital organs open outwardly through ovarian openings 

 situated in the apical system, immediately above the apical extremity of the 

 interambulacral spaces, between the origin of the poriferous zones. There 

 are usually five ovarian openings in all Desmosticha ; passing through large 

 prominent plates, they lead into as many genital organs, consisting of clusters 

 of ovaries or of spermaries. There is no difference in the shape of the gen- 

 ital clusters between the males and the females, beyond the difference in 

 coloring noticed at the time of breeding, when the genital organs are fully 

 expanded. The ovaries arc then usually colored yellowish-brown, while the 

 spermaries an' of a milky tint; they consist of a main tube branching into 

 a number of diverticula filled witb eggs or spermaries. In the Desmosticha 

 the genital organs, at the breeding time, fill the whole of the free space 

 between the test and the alimentary canal in the interambulacral spaces 

 I PI. XXVII. f. ; .■ PI XX VI I If. ;), and the space enclosed within it (PL 

 XXVII f. a; PL XX VIII. f. .:), completely surrounding and encasing the 

 alimentary canal. During the growth of the genital organs they extend 

 as clusters between the test and the alimentary canal i PI. XXVII. f. 2) only 

 in the interambulacral spaces; even at the time of breeding the ambulacra] 

 fields are kept free {PL XXVII. f. 4 ; PL XX VIII. f. 4). 



In the Clypeastroids the genital organs extend over the abactinal part of 

 the alimentary canal (PL XXVIII f. 2 ; PL XXIX.). forcing their way 

 under the inner edge of the outer turn of the alimentary canal, and appear- 

 ing on the actinal floor (PL XXVIIT.f. 1 -. PL XXX.). The course of the 

 alimentary canal can be traced by the compression of the ovaries along its 

 path (PI. XXIX. upper fig. ; PL XXX. lower fir/.). In genera with radiating 

 walls or walls parallel to the outer edge, the ovaries force their way between 

 them, completely filling the intervening spaces (PL XXXI. f. .'). 



In the Petalosticha the genital organs occupy a much more limited space 

 even at the time of breeding (PL XXXII. f. 2, 12), being reduced usually to 

 four small clusters in the abactinal part of the test. In all Petalosticha the 

 genital openings are limited to four, the odd posterior genital opening is 



