78 S. LOVEN, ON POUKTALESIA, A GENUS OF ECHIXOIDEA. 



fice, had reappeared again, the corresponding sexual ghtnd also, in the course of sub- 

 sequent ages, was seen, in some forms, to recover its outlet. This could not have 

 taken place, had not the sexual gland, though checked in its development, and kept 

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

 life, ready to begin its work whenever the repressing influence should have passed. 

 In tlie Ethmolysic Spatangida;', as long as the madreporite is crowding its pores in 

 the restored costal 5, there is no chance for a sexual outlet; but, — assumed that its 

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

 form should be discovered anywhere, in which this migration were accomplished, and 

 the madreporite settled, as a whole, in the interradium 5, it will be a great point to 

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

 demon.strating the hidden existence of the fifth sexual gland, in a still embryonic con- 

 ditidu abiding its time. . 



Organs of vision, — in the whole animal kingdom seen to come forAvard at places 

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

 eign to Crinoidean organisation. In the Asteriadea, on the other hand, their existence 

 has been proved beyond any doubt by Ehrenberg, their discoverer, by H^cckel, Greeff 

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

 ity of each ambulacrum, and, connected with it aborally, a finger-shaped tentacle, 

 both sheltered under the radial, which has been removed from its original site in the 

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

 some '). In the Echinoidea organs apparently identical, but not jet properly studied, 

 are seen in corresponding places, each of the five radials presenting a pore serving 

 as an orbit to the eye '), and close over it a simple tentacle. There both these organs 

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

 eye, PL XIV, fij/. 164, 164 A, and there they are found, out of the field of contest, 

 — for the madreporic filter scarcely ever attains the radials — , in forms geologically 

 old and new, with a tenacity recalling that of the eyes of the Podophthalmous 

 Crustacea, which maintain so invariably their station at the top of the appendages of 

 the first somite, arrested in their development. When in the CoUyrites "'') the bivium 

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

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

 of which the nein-es descend from the central collar to the eyes. 



These are the two principal forms of the calycinal system ])revalent in the great 

 majority of the Spatangidte : the Ethmophracti and the Ethmolysii. A third modifica- 

 tion is of much less frequent occurrence. Paheotropus ^), which by its general outline, 

 its ambulacra all apetalous, similar and level with the [)eris()inc, in some degree re- 



') Etudes p. 8(3, pi. LIII, fig. 256— 2G0. 



•^) lb. p. 66, pi. XI, XII, XV, XVI, XVII, XIX, XXI. 



•') 11). pi. XI, fitr. 98. 



") lb. p. 17, pi. XIII, tig. lOS— 113; Xll. 105; XXXII, 200. 



