The ventricle of the heart of the plaice (Pleuronectes platessa L.) was examined in histological sections stained with Aniline blue. The ventricles from hearts from two age groups (from 3–5 years and 9–16 years as judged from otolith examination) of plaice were studied in histological section. In younger fish (3–5 years) epicardial collagen bundles form a thin (< 24–0 μm) layer and only the superficial trabeculae are partially invested with collagen bundles, those deeper trabeculae not having collagen bundles associated with them. In older fish epicardial connective tissue had increased greatly (> 120.0 μm) in thickness and endocardial collagen is much more abundant, and was observed throughout all ventricular trabeculae. Secondly, in the hearts of older fish only, an extensive epicardial vascular system was observed, as revealed by arterial and venous profiles. This vascular system was confined to the epicardium and did not penetrate the myocardium to form a vascular bed, nor was it derived from extracardiac vessels.

A stereocamera system is described, built-up mostly from commercially obtainable items. Special features include use of standard 55 mm focal length lenses down to 0.5 m focus, adjustable flash duration to improve image resolution, and a visual and audible pinger control for noisy ship conditions. Resolution in tank tests is better than 70 lines/mm, allowing photographs taken in the field to be enlarged to 3 times the natural size of the animals.