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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    467 tentacles nor pigmented grooves. I do not know the habits of this form and never saw it alive, but from the form of the siphon and absence of pigment I doubt if it has any power of vision. Besides the pigmented cells were found other peculiar cells scat- tered here and there through the epidermis to which I will merely call attention. These I have represented in fig. 10; they are clear cells situated between the columnar cells of the epidermis, the nuclei, situ- ated near the tunica seem to be crescent-shape, this however may be due to the action of reagents — these cells are tolerably numerous and could be found in all the specimens that I cut. Summary. In all the forms that I have examined, Spondylus and Pecten pos- sibly excepted, I find that the seat of vision rests in a number of pig- mented epithelial cells, which have at the free end a fine homogeneous cuticle, which is highly.refractive. Although I could find no evidence that nerves were distributed to these cells, it is reasonable to suppose that they are supplied with nerves as are the cells of the general epi- thelial surface. Now when we compare these cells with those found in the eyes of Patella, situated at the base of the tentacles, we find here a similar state of affairs. As is shown by Fraisse i, the eye of Patella is a simple invagination of the epidermis, forming a sac which is open exteriorly, and allows free access to the surrounding medium, water. Fkaissb could find no evidence of nerves being distributed to this organ. The pigmented cells which lined this invagination were supplied with nerves that were distributed to the general epithelium as was the case with the LamellibrancMata, that I examined. The pig- mented cells, which make up the eye of Patella (fig. 12), have es- sentially the same form as those found in the LamellibrancMata. Now in the LamellibrancMata we have even a simpler form of visual organ than that of Patella, for in Patella we have the organs specialized in number, two, and situation - in the base of the tentacles at the anterior or oval end of the beast. In the Asiphonata the vision is very general- ized—patches of pigmented cells scattered at large at that portion of the animal most exposed to light and danger. A somewhat higher grade is seen in the Siphonata, where the pigment is more localized in the lower 1 P. Fraisse, liber Molluskenaugen etc. 1881. 31*