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Keywords:

  • Dall's porpoise;
  • Phocoenoides dalli;
  • retina;
  • ganglion cell;
  • resolving power;
  • tapetum lucidum;
  • collagen

Abstract

The structure of the retina, the distribution of ganglion cells, and the extent of the tapetum lucidum were studied in Dall's porpoise (Phocoenoides dalli) with the aim of understanding the role vision plays in this species of cetacean. The basic organization of the retina was similar to that of other vertebrates. Average ganglion cell size was 21.5 μm. The distribution of the ganglion cells in the retina was not even and there were two high-density areas, one in the temporal and one in the rostral part of the retina. Retinal resolving power was estimated using a terrestrial animal model incorporating the density of ganglion cells and other morphological data. The resolving power in the right eyes of two individuals was 2.60 and 2.64 cycles per degree. These values were close to those of other oceanic cetaceans, but inferior to those of terrestrial mammals. On the basis of amino acid analyses, it was shown that the choroid tapetum lucidum in Dali's porpoise contained collagen. The tapetum lucidum was thick at the fundal but thin at the peripheral part of the choroid.