438 Prof. S. Lov^n on the Structure of the Echinoidea. 



sequence ; the fasciola is still an unexplained organ. It has a 

 border-line (" SaumUme''^), says Johannes Miiller, comparable 

 with the ciliary border of the larva in these respects, that it 

 forms closed loops and produces an extremely brisk ciliary 

 movement. Its satin-like close clavulse of equal height, the 

 shafts of which, and not the rounded and soft heads, are the 

 vibratory organs, as was already observed by Johannes Miiller, 

 are in a his-h deofree sensitive : and if a few of them are touched, 



• TTT" 1 



many pass instantly into a common wavnig movement. With 

 respect to the important question whether the Echinoderm has 

 taken this over from its larva, and the membrane bounds it, it 

 is worth remembering that the infraanal fasciola and the lateral 

 (Desor) exclude each other. 



On the dorsal surface, in all recent Echinoidea, the five 

 ambulacra and the five interradia meet at a circle of five 

 occllar plates and, typically, five vertical plates. The latter 

 have been called genital plates, because, in most cases, the 

 efferent ducts of the genital glands have their external aper- 

 tures, the genital pores, in them, and they have been regarded 

 as belonging to the organs of reproduction. But they are no 

 more a part of these than the plates of the unpaired interradium 

 are a part of the nutritive organs because in the irregular 

 Echinoidea the anus perforates them. It is easy to ascertain 

 that the plates which have here hitherto been named vertical 

 plates are present and ready formed in young individuals 

 which are not yet fertile, and to observe how it is only at a 

 later period, when the genital glands are matured, that their 

 efferent ducts, oviducts, or vasa deferentia, perforate the plates 

 from within. The madreporite, on the other hand, is com- 

 menced early during the larval state, and is undistinguishable 

 from the vertical plates, while the genital pores in certain 

 cases are distant from them. The greater the part occupied 

 in tlie vertical plates by the aquiferous system, the smaller is 

 that of the genital organs ; and, vice versa, when tlie former is 

 small the latter is large. In the Spatangidae the genital pore 

 is wanting in the plate towards which the percolating appa- 

 ratus spreads from its central region — so far, that of the nor- 

 mal five never more than four remain, in some not more than 

 two. When, as in Laganum, the madreporite, which in some 

 species of that genus opens into a ramified fissure, occupies the 

 middle of the stellate ring, or, as in Echinocyamus, it consists 

 only of a single pore, and when, besides, as in both these 

 genera, the interradia close with one plate of the last pair very 

 large and wedge-shaped, the genital pores in the vertical plates 

 are situated near their margins ; but when the madreporite is 

 more widely expanded, so that it occupies the whole star of 



