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 2 1.5 hm. 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 rostra1 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.

In several teleost fishes, guanine type ocular tapeta lucida were studied by conventional light and fluorescence microscopy. Retina1 tapeta lucida were found in the eyes of Chlorophthalmus albatrossis, Chlorophthalmus nigromarginatus, Chlorophthalmus acutifrons, Beryx splendens, Beryx decadactylus, Polymixia japonica and Polymixia bemdti. Choroidal tapeta exist in the eyes of Neoscopelus microchir, Diaphus coeruleus, Diaph us sagarniensis, Epigon us atherinoides, Priacanthus macracanthus, Priacanthus harnrur, Priacanthus boops and Pn'stigenys niphonia. Spectrophotometric and paper-chromatographic evidence reveals the tapetal material to be mainly guanine. Grouped receptors in the retinas of Chlorophthalmus and Polymixia and argentea in the eyes of Priacanthus are described and a classification of the tapeta lucida in teleosts is given. The relationship between retinal and choroidal tapeta is discussed and a possible explanation offered for the two types of tapetal organization in teleosts. Apparently, the two types are related to the ecology and behavior of the species concerned.

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The sonic motor nucleus and its fiber connections were examined in a rockfish, Sebastiscus marmoratus by means of tracer methods using horseradish peroxidase (HRP), biocytin, and carbocyanine dye (DiI). Sebastiscus has a swimbladder and a pair of extrinsic sonic/drumming muscles. The sonic muscle is ipsilaterally innervated by the occipital nerve which is composed of two ventral roots arising from the sonic motor nucleus. The sonic motor neurons are distributed in the most ventral part of the ventral column from the caudal medulla to the rostral spinal cord, and form a ventrally located columnar nucleus. Each neuron in this nucleus possesses a long thick dendrite and several short dendrites. The long dendrite extends dorsolaterally and branches in the lateral funiculus, whereas the short dendrites branch around their cell bodies. After biocytin injections into the sonic motor nucleus, two groups of premotor neurons were retrogradely labeled bilaterally, one in the dorsomedial portion of the descending octaval nucleus (DO) and the other in the medial zone of the reticular formation (RF) in the medulla. The DO premotor neurons were multipolar with several dendrites branching near the cell bodies, and the RF premotor neurons were bipolar. One of the two dendrites of the RF premotor neurons extends laterally into the ventral portion of the DO, and the other dendrite extends into the ventromedial area in the medulla. In the ventromedial dendritic field of the RF premotor neurons, descending fibers arising from the optic tectum (TO) and torus semicircularis (TS) traverse in the tractus tectobulbaris and terminate bilaterally. After DiI insertion into the ventromedial dendritic field, retrogradely labeled neurons were found bilaterally in the TS and TO. The majority of tectal neurons were located in the stratum griseum centrale. These neurons had two short basal dendrites branching in the cell layer and a long apical dendrite extending to the stratum fibrosum et griseum superficiale and stratum opticum. The toral neurons were bipolar and were distributed throughout the TS. Furthermore, biocytin injections into the medial nucleus of the lateral line system revealed that the nucleus projects bilaterally to the RF premotor neurons. These results show that premotor neurons for the sonic motor nucleus are located in the dorsomedial portion of the DO and the medial zone of the RF in the medulla. It is suggested that the sonic motor nucleus receives auditory input via the DO premotor neurons and input from RF premotor neurons which receive lateral line input via the medial nucleus, vestibular input through the lateral dendrite extending into the ventral portion of the DO, and information from the TO and TS via the tractus tectobulbaris.