452 Benjamin Sharp 



irregulär rows. Inside of the inner row of tentacles is found a pìg- 

 mented band dififering greatly in intensity in different individuals. 



I bave sought in vain for any appearance of distinct eyes in this 

 part , or in any part , of the mantle ; and further none bave been re- 

 vealed by studying carefully a complete series of sections of the mantle- 

 border. 



It has been asserted by Garner , Will and Siebold that Ostrea 

 possessed eyes of great complexity. They may bave examined certain 

 forms that 1 bave been unable to obtain , but as far as Ostrea virginica 

 and O. edulis are concerned , I can state that no complex eye exists, 

 uor any evidence to siipport their assertions. That these aniraals 

 possess a limited power of vision there is no doubt, as it has been as- 

 serted by my friend Mr. J. A. Ryder i, a most careful observer, that 

 when a shadow passes over the extended edge of the mantle it is in- 

 stantly retracted. 



I will now take np the minute anatomy of this part, and endeavour 

 to point out the seat of vision. 



When a vertical section of the anterior border of the mantle is 

 made we find the free edge thrown into three distinct folds (fig. 1 a, i, e). 

 These are evidently longitudinal sections of the tentacles already spoken 

 of. At the base of the centrai fold [h) is seen the transverse section 

 of the large circumpallial nerve (fig. 1 P.N.). This nerve according to 

 DuvERNOY^ Comes from the principal or posterior ganglion. In the 

 same section it can be seen giving off branches into the tentacles. The 

 circumpallial nerve does not consist entirely of nerve fibres, but ganglion 

 cells may be seen scattered through it. 



The body of the mantle is composed of muscular and connective 

 tissue fibers, which cross each other in ali directions, and imbedded 

 in them may often be seen distinct nuclei. Between these fibers may be 

 seen the blood Spaces or lacunae (fig. 1 h.s.) . 



Passing through this mass of connective tissue, perpendicularly to the 

 circumpallial nerve is seen a bündle of muscular fibers (fig. 1 r.m.]; this 

 bündle divides and, when a series of consecutive sections are examined, 

 they may be seen to become fastened to the epithelial layer that forms 

 the external covering of the whole mantle. One brauch , seen in the 

 figure (fig. 1 d), passes to the base of one of these folds. These bands 



' J. A. Ryder, Primitive visual Organs. Science. Voi. II. Cambridge, Mass. 

 1883. p. 739. 



- DuvERNOY, Mém. s. 1. syst. nerv. etc. 1854. p. 55. 



