The harp seal, Pagophilus groenlandicus (Erxleben, 1777). VI. Structure of retina

• Published in: Canadian Journal of Zoology
• Main Authors: Nagy, A. R., Ronald, K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1970
• Subjects: Harp Seal; Pagophilus groenlandicus
• Online Access: http://dx.doi.org/10.1139/z70-058; http://www.nrcresearchpress.com/doi/pdf/10.1139/z70-058

The retina of the harp seal (Pagophilus groenlandicus) was studied by means of the light microscope. Ganglion cells occupy a single layer. Thinly dispersed throughout this layer are giant ganglion cells. There is no area centralis. The inner nuclear layer consists of large horizontal cell processes with bipolar and amacrine cells between the horizontal cell processes. The outer nuclear layer is the thickest of all retinal layers. Its density is constant in the central and peripheral areas of the retina, similar to that found in the inner nuclear and ganglion layers. Only rod photoreceptors were found; therefore it is presumed that seals have no color vision. The tapetum covers an extensive area and is 32–34 cellular layers thick centrally, diminishing in thickness peripherally. The combination of tapetum and rod receptors makes possible excellent visual sensitivity to dim light.