| Summary: | Haemochromogen from the crop of Helix pomatia was partially purified. The preparation had a minimal weight of 140,000. Its spectrum was studied, and compared with that described by previous workers. Confirmation was found for its being a protohaemochromogen. The preparation was fully autoxidisable at all pH values. A survey showed that protohaemochromogens were ofcommon occurrence in the Mollusca and tubicolous Polychaeta, but were rare in the Crustacea. All the Polychaeta examined, with exception of the Chaetopteridae, had protohaemochromogen, or other protohaem in the gut. The survey suggested that gut haemochromogens were derived from the animals in which they were found. The concentration of haemochromogen in the crop of Helix aspersa was found to vary profoundly with the activity of the animal, and with the state of digestion of the food, but little with the nature of this food. In Daphnia magna the concentration of haemochromogenin the interior hart of the gut was found to vary with the activity of the gut, and the concentration of body haem. Under favourable culture conditions, an external factor(s) was necessary for its production in mature animals. A relationship was found between the concentration of gut haemochromogen and that of the haem respiratory pigment in the blood. In certain Polychaeta an inverse correlation was established between the concentration of gut haemochromogen (or haem) and that of the haemoglobin or chloro-cruorin in the plasma. In Daphnia, the gut haemochromogen and haemoglobin concentrations were found to vary inversely in favourable, and directly in unfavourable conditions. This may have been a secondary relationship, the true one being with the tissue protohaem. Results suggested that in Daphnia gut haemochromogen may be derived from tissue protohaem, but that under certain conditions it may be formed as an alternative to the latter.
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