78 S. LOVEN, ON rOURTALESIA, A GENUS OF ECHINOIDEA. 



ficc, bad reappeared again, the corresponding sexual gland also, in the course of sub- 

 sequent ages, was seen, in some forras, to recover its outlet. Tbis could not have 

 taken place, bad not tbe sexual gland, tbougb checked in its development, and kept 

 back in a rudimentary state, continued, during a genetic succession of forras, its dormant 

 life, ready to begin its work whenever tbe repressing inHuence should bave passed. 

 In tbe Etbraolysic Spatangida3, as long as tbe raadreporite is crowding its pores in 

 tbe restored costal 5, tbere is no chance for a sexual outlet; but, — assumed tbat its 

 raoveraent across the old boundary is in earnest the beginning of a migration, — if a 

 förra should be discovered anj^wbere, in wbich this raigi^ation were accoraplished, and 

 the raadreporite settled, as a wbole, in the interradiura 5, it will be a great point to 

 look for the return of the sexual outlet. Meanwhile the problem is near at hand of 

 deraonstrating the bidden existence of tbe fiftb sexual gland, in a still erabryonic con- 

 dition abiding its time. , 



Organs of vision, — in tbe wbole animal kingdom seen to corae forward at places 

 of commanding situation, irrespectively of morpbological relations — , appear to be for- 

 eign to Crinoidean organisation. In tbe Asteriadea, on tbe other hand, tbeir existence 

 bas been proved beyond any doubt by Ehkenberg, tbeir discoverer, by Hackel, Greeff 

 and others. A group of crystalline cones surrounded by pigment is seen at the extrera- 

 ity of eacb ambulacrum, and, connected with it aborally, a finger-sbaped tentacle, 

 both sheltered under the radial, wbich bas been reraoved from its original site in the 

 axillary angle between two costals, by the interposition of the largely developed peri- 

 sorae ^). In the Echinoidea organs apparently identical, but not yet properly studied, 

 are seen in corresponding places, eacb of the tive radials presenting a pore serving 

 as an orbit to the eye "), and close över it a siraple tentacle. Tbere both these organs 

 appear very early, even before the madreporic filter, and the tentacle perbaps before the 

 eye, Pl. XIV, fig. 164, 164 A, and tbere they are found, out of the field of contest, 

 — for tbe madreporic filter scarcely ever attains tbe radials — , in forras geologically 

 old and new, with a tenacity recalling tbat of tbe eyes of the Podopbthalraous 

 Crustacea, wbich maintain so invariably tbeir station at tbe top of the appendages of 

 the first soraite, arrested in their developraent. When in tbe Collyrites ^) tbe bivium 

 is severed frora the calycinal system through the interposition of the enlarged inter- 

 radia 1 and 4, the radials I and V adbere to tbe respective ambulacra, on tbe insides 

 of wbich tbe nerves descend frora tbe central collar to the eyes. 



These are the two principal forms of the calycinal system prevalent in the great 

 majority of the Spatangidaa : the Ethmopbracti and tbe Ethraolysii. A third raodifica- 

 tion is of raucb less frequent occurrence. Palajotropus *), Avbich by its general outline, 

 its ambulacra all apetalous, sirailar and level with tbe perisorae, in some degree re- 



1) Études p. 86, pl. LIII, fig. 256—260. 



-) Ib. p. 66, pl. XI, XII, XV, XVI, XVII, XIX, XXI. 



3) Ib. pl. XI, fig. 98. 



") Ib. p. 17, pl. XIII, fig. 108—113; XII, 105; XXXII, 200. 



