KONGL. SV. VET. AKADEMIENS HANDL. BAND. 19. N:0 7. 77 



In like inanner the conception of the costals as »genital plates» on a closer in- 

 spection ceases to be teiiable. Subsequeritly to the appearance externally, in the young 

 Echinid, of the madreporic filter, when the reproductive glands approach inatnrity, 

 their efiferent ducts penetrate from within the costals, and, in the adult state of the 

 great majority of species, a sexual pore is found in each of these. To this there are 

 but rare exceptions, such as Goniopygus, but in the Clypeastridaä not a few forms have 

 their sexual apertures outside the costals, in the respective interradia '). In the En- 

 docyclic Gnathostomes all the five costals are perforated, but four only in the earliest 

 among the Exocyclic, in Pygaster, the fifth having disappeared along with the costal 

 5, at the outbreak of the periproct. And, thougb in Oolitic species of Holectypus 

 the costal is restored, it is not until in the Cretaceous era that its pore reappears ^), 

 just as in DiRcoidea, of early Cretaceous oi^igin, it reverts only in the Turonian time, — 

 and this is the last instance known of its reinstatement, for among the Echinoneidaj 

 and Cassidulidfe it never reappears. In these last-named the four sexual pores are far 

 asunder, owing to the central expansion of the madreporite, they are drawn near to- 

 gether laterally in the narrowed and lengthened calycinal system of the Gollyrites and 

 in the Meridosternous Spatangi, such as Anancites, Hemipneustes and others, and they 

 are squared again in the shortened system af the Amphisternous Ethraophracti. In the 

 Spatangida; Ethmolysii, also, four is their normal number. In some cases, for instance 

 in Spatangus purpureus, they seem to make their appearance very irregularly, all four 

 being present in a specimen of the stage mm. 1-5 : 14, Pl. XVIII, fig. 213, but wanting 

 in another of mm. 16:15, Jig. 214, almost so even at mm. 19 : 18, _/?(/. 216, highly 

 developed at mm. 23 : 22, fig. 218, while the two anterior are only indicated in a spe- 

 cimen of mm. 24:21. fig. 217, — anomalies that possibly are apparent only, and may 

 depend upon difference of sex. During the growth, also, one or even two of the pores are 

 liable to give way in the struggle against the madreporite. In the costal 2, the old 

 site of the filter, this not seldom prevails and causes the sexual pore to abort, some- 

 times accidentally, as in Brissopsis lyrifera, Pl. XIX, fig. 229, but regularly in certain 

 species of Schizaster, as Sch. fragilis D. & K. 'j, Sch. Moseleyi Al. Ag., in Tripylus, 

 and in Abatus cavernosus Phil., Pl. XVIII, fig. 220. In Abatus Philippii n. ^), in 

 Moira atropos Lamk., and in some other species of Schizaster, as Sch. canaliferus Lamk., 

 Sch. jiiponicus Al. Ag., it has disappeared in the costal 3 also. But among the Spa- 

 tangidge the sexual organs are never deprived of their outlets in the costals 1 or 4 



Thus the madreporite, with its internal apparatus of cavities, passages and ca- 

 nals combined into a solid calcified structure, by its expansion and regressive move- 

 ment determines, in the Spatangida3, the closing up of one or raore of the sexual 

 openings, and constantly that of the costal 5. In earlier types, when this same costal, 

 uppressed for a time in consequence of the retrograde passage of the excretory ori- 



^) Études, p. 80, Pl. XVI, fig. 136. Ib. p. 69. Cotte.iu Pekon et Gauthiee, Échinides de TAlgérie, V, 



p. 223, Pl. XVI, fig. 1—12. 

 ■^) See above, woodcut p. 68. 



^) Études, pl. XII, fitf. 102. In Sch. gibberulus Ag. all four sexual pores are present. 

 ') Ib. pl. XI, fig. 99. 



