THE UYI)K()SI'li;i:s AM) Sl'IK.U'LKs. Si 



Except for this suggestion, no contributions were made to the morphologj of the 

 hydrospires for more than ten years alter Billings wrote. But their respiratory 

 function was generally recognized, and Billings's names " hydrospires " and "spira- 

 cles" were adopted as convenient and expressive. 



The Canadian author seems to have altogether abandoned the theories of Say and 

 his successors as to the genital function of the peripheral summit-openings. Mosl 

 writers were inclined to compare them to the genital openings in the apical system 

 of Echinus, which are dorsal in position, while those of the Blastoids are ventral. 

 Edward Forbes 1 remarked, however, that they correspond very closely in position 

 with the genital openings of a Starfish, and more especially with those of Ophiurids 2 . 



Forbes supposed that one pair of the ovarian pons was suppressed in consequence 

 of the anal pore being brought near to the mouth, whereas in the Starfish it remains 

 on the dorsal surface. Roemer 3 pointed out, however, that the fifth pair is present 

 in Pentremites, but concealed within the large anal opening ; and he further stated 

 that in consequence of the manner in which the hydrospire-apparatus opens exter- 

 nally by the spiracles it must be regarded as " Behalter der Eierstocke und Eileiter.'* 

 But he remarked that in this case the Blastoids would differ very much from the 

 Crinoids, for Miiller's observations had shown that the genital glands of Pentacrinus 

 and Gomatula are situated in the pinnules. White 4 followed this up by saying that 

 if the tubular openings of Pentremites " are to be regarded as ovarian apertures, it 

 will be necessary, as before remarked, to disregard the close analogy of these animals 

 with the true Crinoids, in which the ova are developed in little accessory sacs at the 

 base of each tentacle, between which organs and the summit tubes of this species 5 

 there is no connection and apparently no indication that any ever existed. It seems 

 more probable that as the ova were germinated within the body they found their 

 exit through the central summit aperture, and were conveyed along the small central 

 grooves of the pseudambulacral fields, before mentioned, to the bases of the tentacula, 

 where they were developed and discharged as in the true Crinoids." White's theory 

 was based essentially upon the fact that the central opening of the summit could not 

 be the mouth, owing to its being covered up by the small plates of the vault, and 

 he was therefore led to regard it as ovarian in function. There can be no doubt, how- 

 ever, that the central opening was the mouth, and that the ambulacral grooves were 

 lined by cilia, all working towards it ; so that the currents of water converging on 



1 " On the C'ptidcse of the Silurian Rocks of the British Islands," Mem. Geol. Survey Great Britain, 

 1848, vol. ii. part ii. p. 529. 



2 The Pentremites pentagonalis employed by Forbes in this comparison seems to have been a C'odaster 

 or PlwnoscJiisma, which have no genital openings at all ; though he was led to insert them into his diagram 

 from his knowledge of their presence in the true Pentremites. 



3 Archiv f. Xaturgesch. 1851, Jahrg. xvii. Bd. i. p. :344. 



4 Journ. Bost. sk>r. Nat. Hist. lMi3, vol. vii. no. 4, p. 4S5. 5 Q-ranatocrinus Nbrwoodi. 



11 



