Vital staining with Janus Green, phase contrast and scanning electron microscopy were used to map the distribution of free neuromast organs from first hatching, 10 mm long larvae to 100 mm long juveniles of herring (Clupea harengus L.), with some further observations on juvenile sprat (Sprattus sprattus (L.)). Neuromasts are sparsely distributed on the head and trunk at hatching but soon proliferate on the trunk where, by a length of 13–15 mm, they occur one to every segment. Near metamorphosis there are at least three rows of neuromasts on the anterior trunk region, 6–9 single neuromasts on the caudal fin and as many as 50 on the head. The scales develop at about 40–50 mm and the neuromasts are then found singly or in groups of 2 or 3 on the surface of the scales of the anterior trunk.The lateral line develops at 22–24 mm and appears to incorporate existing free neuromasts on the side of the head. Unlike the cupulae of the free neuromasts, which are cylindrical, the lateral-line cupulae are thin erect plates lying along the axis of the canals. They are probably continually growing and being shed, followed by renewed growth.All neuromasts contain hair cells of opposing polarities; most free neuromasts are arranged with these polarities arranged fore-and-aft, but a few are dorsoventral.

Bony fishes belonging to 75 families were examined for ocular tapeta lucida. The results are collated with published records, and tapeta are shown to occur in 28 families of teleostomes (Holostei and Teleostei) listed in Table 2. Except in the bigeyes Priacanthidae, they are diffuse reflectors located in the pigment epithelium. Based on chemical composition, several types can be distinguished, lipid, guanine (purine), and some others, colored yellow or light tan, of unknown composition. In several tapeta minutely examined, the reflecting material occurs as platelets (guanine type) or as minute tapetal spheres (lipid and others). The tapetum of the bigeye lies in the chorioid, it is a specular reflector containing guanine; as such it is the solitary known exemplar among teleosts.

Various workers during the past century have figured sensory cells bearing cilia amongst the ordinary non-ciliated epidermal cells of the body surface. Similar sensory cells were also found on the buccal cirrhi, and on the velar tentacles at the entry to the atrium. This earlier work at the light microscope level was summarized by Franz (1923) in his excellent review. More recently Schulte & Riehl (1977) have re-examined the innervation of the oral region and buccal cirrhi at the ultrastructural level, and observed two types of sensory cell in these regions, distinguished by their apical structure. They suggest that these are both secondary sensory neurons (as Franz had previously surmised), but their figures hardly make this suggestion convincing. In this note we show that there is probably only a single type of sensory cell amongst the epidermal cells of the body surface and buccal cirrhi; that it synapses at its base with incoming axons of central cells, and that a different type is indeed found in amphioxus, but only in the velar tentacles.