i U.WloclMXrs DIOMKD K. 



b) Ludwig,* as they are based upon conditions found in the adult. 

 Ho has taken as Ins guide the position of the anus, which, as is well known, 

 does not hold a lixod position, but occupies an indefinite place, in the anal 

 system of Echini. See the figures of the anal systems of a number of 

 Echini given by Loven in his Etudes, and by myself in the Revision 

 of the Echini. t 



Embryological investigations have proved beyond a doubt that the 

 platos which are called ocular, genital, madreporic, and anal in the Echini, 

 and genital and madreporic in the Starfishes and Ophiurans, have no or- 

 ganic connection with the genital or water systems. The plates have 

 received the above denominations from being in early stages of growth 

 connected with the ocular,:}: genital, or water systems. A similar want of 

 connection between the so called anal system and the anal opening, and 

 the shifting position of the madreporic body, has been traced by palaeon- 

 tologists, and followed out in great detail by Loven in his Etudes and 

 in his Pourtalesia. The unstable position of the madreporic body, of the 

 genitals, and of the anal opening, for different periods in the palseon- 

 tological development of the Echini, had been insisted upon before him 

 by writers on the classification of recent Echini. 



* Ueber den primiiren Steinkanal der Crinoiden nebst vergleichend anatoniischen Bemerkungen 

 uber die Echinodermen iiberhaupt. Zeitschr. f. Wiss. Zool., XXXI V. 



f Carpenter (On some disputed Points in Echinoderm Morphology, Quart. Journ. Micr. Sci.. July, 

 L880, XX. :;_'l) has already called attention to the many difficulties in the way of adopting the new 

 homologies suggested by Lndwig. 



I The nature of the odd terminal ambulacra! tentacle of the young stage of Echinidie has not been 

 investigated, so that no comparison of function can be made between it and the odd terminal tentacle 

 which carries an eye spot in the young Asteridre. A. Agassiz, Embryology of the Starfish, 1864. 



These eyes persist in the old stages of the Starfish, and have been described by many authors since 

 the time of Ehrenberg (Ueber die Akalephen des Itothen Meeres), who first called attention to their 

 existence. 



Forbes in his History of the British Starfishes (1841, p. 152) speaks of the perforations of the 

 smaller cordate plates which separate the ovarian plates as filled with a red membrane or substance, 

 and he regards them as analogous to the so called eyes of the Starfish. 



Valentin says : " Je dois avouer que jusqu'a present toutes mes tentatives pour decouvrir une lentille 

 dans cet organe ont etc vaines. Je n'y ai trouve qu'un corps pigmente compose de diffe'rents tissus 

 fibreux et celluleux. Une seule fois j'ai cru y decouvrir, dans an exemplaire de l'E. lividus, con- 

 serve dans lesprit de vin, un organe globuleux adherant a une tige." Anatomie du Genre Echinus, 

 1841, p. 100, Plate IX. Fig. 190. 



It is exceedingly interesting to note that the only organs which may be called eyes which have as yet 

 been described in Echini should be placed on the surface of the test, either in continuous lines, or in 

 spots in the interambulacral areas, and that these so called eye spots should not be found on what echi- 

 nologists have been in the habit of calling ocular plates. They exist on the genital plates and on some 

 of the plates of the anal system. See for their description the careful investigations of the Sarasins, in 

 Ergebnisse naturwissenschaftlicher Forschungen auf Ceylon, von Dr. Paul Sarasin und Dr. Fritz 

 Sarasin, Erstes Heft, 1887. Die Augen u. das Integument der Diadematiden, pp. 1-17, Pis. I.— III. 



