334 S. WATASE. 



VI. — Api'knuix. 

 7'Ae Comjyound Eye of Echinoderms. 



While tlie proecding paper on the compound eye of Arthro- 

 pods was passing through the press I improved my opjjor- 

 tunity to study the compound eye of Ecihinodcrms at Woods 

 Holl, during the months of June and July, 1SS9, to see how far 

 the morphological interpretation advanced for the former will 

 hold to the latter. 



The three starfishes common at Woods Holl, viz. Asterias 

 vidgaris, StiiTip., Asterias forhesii, Verril, and Cribella sangui- 

 nolenta, Lutken, were studied in this connection. While T 

 reserve the description of tlie details for a future paper, I will 

 briefly point out some important bearings of the results upon 

 the subject which has been discussed in the preceding pages. 



The general structure of the compound eye of the starfisli at the 

 tip of each ray is well known through the writings of HiKckel, 

 Wilson, Hoffmann, Lange, Greeft', Hamann, Carri&re, and some 

 others, althougli there exist some discrepancies in regard to the 

 histological features of the organ as described by these natura- 

 lists. 



The most remarkable observation on the eye of the Echino- 

 derm among the early writers is that of Goodsir, who, according 

 to Forbes,' is said to have examined the eye of Cribella oculata 

 and remarked of its structure that it consisted "o/' a red cushion 

 with pits on its surface.'''' My studies on the compound eyes of the 

 starfishes convinced me of the truth of Goodsir's statement, and 

 the eye of a starfish is nothing more than a group of ectodermal 

 conical pits with their bases turned towards the exterior. The 

 epithelial cells which form the walls of the conical pit have each 

 a cuticular rod secreted at the tip of its distal extremity. 



These cells send out nerve fibres from their proximal extrem- 

 ities. In the centre of the pit along the longitudinal axis 

 of the invagination there is a space filled with a clear fluid sub- 

 stance. The cuticular secretions of the retinal cells, as well as 

 the colorless fluid substance, constitute together a translucent 



' E. Forbes : A Tlistory of Briligh Slarfiishes, and other Animals of the class 

 Echinodermala. London, 1841, p. 103. 



