84 CATALOGUE OP THE BLASTOIDEA. 



marsupial pouches; while Ludwig \ to whom Studer's observations were unknown, 

 named them genital bursas, in consequence of their relation to the apparently isolated 

 genital tubes which he found to be in reality the fertile portions of an extensively 

 ramifying genital gland enclosed within a blood sinus, just as in the Crinoids. These 

 genital organs are always situated " mit ganz kurzen Ausfiihrungsgangen der Bursa 

 in der Nahe ihrer Eingangsspalte an, wahrend die blindgeschlossenen Endzipfel der 

 Bursa? keine Genitalorgane tragen." 



Ludwig regards these organs as internal gills, comparable to the external gills of 

 the Starfish, the contents of the body-cavity being brought into direct relation with 

 the external water in each case. He further points out that the position of the genital 

 organs in the immediate neighbourhood of the external slits shows that the more 

 internal portions of the bursa? must have had other functions than merely to serve 

 for the discharge of the genital products, while their presence in sexually immature 

 individuals and in males goes to show that they are not exclusively marsupial organs. 

 The position of these genital slits at the sides of the ambulacra in Ophiurids is so 

 remarkably like that of the so-called spiracles in Orophocrinus stelltformis (PI. XI. 

 fig. 9), that Ludwig was led to compare the hydrospires of the Blastoids with the 

 bursas of the Ophiurids ; and he pointed out that the inner wall of the latter, i. e. 

 that next the body-cavity, is more or less plicated and frequently strengthened by 

 calcareous deposits. We regard this suggestion of Ludwig's as an exceedingly happy 

 one, and are entirely of the opinion that the hydrospires of the Blastoids served both 

 for the purpose of respiration and for the discharge of the genital products. Oropho- 

 crinus has but one slit at each side of the ambulacrum (PI. XL figs. 8, 9 ; PI. XIV. 

 fig. 16; PI. XV. figs. 2, 4, 5, 8, 10, 11, 13), like most Ophiurids; but in the genus 

 Ophiura there are two slits opening into the same bursa, and occasionally separated 

 from one another by some little distance, owing, as Ludwig puts it, to the approxi- 

 mation of the lateral walls of the primitively single cleft about the middle of its 

 length. This is somewhat comparable to the difference between Orophocrinus and 

 such a type as Cryptoblastus melo (PL VII. fig. 15), in which last the hydrospire-cleft 

 is completely closed for some little way behind the spiracle owing to the lancet-plate 

 coming into immediate and close contact with the deltoids. But along the sides of 

 the radials the hydrospire-clefts open out again and each communicates with the 

 exterior by a line of pores, owing to its being crossed by a series of small bridges 

 between the hydrospire-plate and the side of the radial. Apart from this fact, how- 

 ever, there are two openings into each hydrospire-sac, an aboral and an adoral one, 

 just as in Oplriura. 



Unaware of Ludwig's happy comparison between the genital bursas of an Ophiurid 

 and the hydrospire-sacs of a Blastoid, Hambach has made some rather singular state- 



1 Loc. eit. pp. '273-282. 



