326 S. WATASE. 



Ilamann,' who studied this structure in Echinus, dechires tliat 

 the so-ciilled " eye-spot " in the sea-urchin Vwars a close resem- 

 blance to the terminal feeler at the tip of arm of a starfish, with 

 which he thinks it is homologous and not with the eye. He 

 therefore substitutes the term " intergenital plate" for the 

 "ocular plate" upon which this problematical organ rests. 



Even if this organ be shown to have some connection with the 

 visual function, as Romanes and Ewart- claim on the ground 

 of their experiments, it is safe to say that it belongs to a 

 different category of visual organ, as Hamann's histological study 

 clearly shows, and has nothing to do with the subject under our 

 consideration, viz. the morphology of the covqxnmd <??/eofthe 

 Echinoderm and the Arthropod. 



Entirely apart from the preceding, but which may be mentioned 

 in this connection, is the Sarasins' discovery' of the compound eyes 

 in a sea-urchin {Diadema) from Ceylon. Of their visual nature 

 there can be no doubt, as their experiments on the living animals 

 as well as the anatomical structure of the eyelet show. 



The eyelet of the compound eye in Diadema is very much 

 more complex than that of the starfishes I have examined. I 

 cannot help but believe that a study of development of such an 

 interesting form as Diadema, as well as a more extensive study 

 of the eye in different genera and species of Echinoderms, will 

 throw a great deal of light on the morphology of the compound 

 eye in general. 



In my main paper on the subject I hope to describe in detail 

 the structure and development of the compound eye of the star- 

 fish that I have studied, and also to give an account of the 

 growth of our knowledge of the visual organ of the Echinoderms, 

 both anatomical and experimental, from Tiedman and Ehrenberg 

 down to the present day. 



'Ilamann, Otto: Beilruge zur Eiaiologie der Echinodermen. Jenaische 

 Zeitschrift fur Naturwissensohaft, Bd. 21, 1887, pp. 124-136. 



' Romanes, J. Q., and Ewart, J. C. : Observations on the Locomotor System of 

 JEchiiwdermata. Philosophical Transactions, Royal ^ociety, London. Pt. Ill, 

 1881, pp. 855-856. 



'Sarasin, P. B. and C. F. : Uebereinen mit Ziisammengesetzten Augenbedeckten 

 Seeigel. Zoologischer Anzeiger, 8 Jahrg. No. 211, 1885. Their main paper I 

 bare not seen. 



