On the visual organs in Lamellibranchiata / by Benjamin Sharp.

  • Sharp, Benjamin, 1877-1916.
Date:
[1883]
Catalogue details

Licence: Public Domain Mark

Credit: On the visual organs in Lamellibranchiata / by Benjamin Sharp. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    irregular rows. Inside of the inner row of tentacles is found a pig- mented band differing greatly in intensity in different individuals. I have sought in vain for any appearance of distinct eyes in this part, or in any part, of the mantle; and further none have 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 have examined certain forms that I have been unable to obtain, but as far as Ostrea virginica and 0. edulis are concerned, I can state that no complex eye exists, nor any evidence to support their assertions. That these animals possess a limited power of vision there is no doubt, as it has been as- serted by my friend Mr. J. A. Ryder1, 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 up 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, b, c). These are evidently longitudinal sections of the tentacles already spoken of. At the base of the central fold [b] is seen the transverse section of the large circumpallial nerve (fig. 1 P.N.). This nerve according to Duvernoy 2 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 all directions, and imbedded in them may often be seen distinct nuclei. Between these fibers may be seen the blood spaces or lacunae (fig. 1 b.s.). Passing through this mass of connective tissue, perpendicularly to the circumpallial nerve is seen a bundle of muscular fibers (fig. 1 r.m.); this bundle 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 branch, seen in the fi-ure (fig. 1 d), passes to the base of one of these folds. These bands i J.A.Ryder, Primitive visual organs. Science. Vol. II. Cambridge, Mass. 1883. p. 739. 2 Duvernoy, Mem. s. 1. syst. nerv. etc. 1854. p. 55.