Endocrine Control in the Crustacea

Abstract

SUMMARY The hormones of crustaceans may be grouped into those which control effector organs (chromatophores, muscles) and those which control the more gradual sequences of growth, development and reproduction; they have been termed energetic and metabolic hormones respectively. Most of the known crustacean hormones originate in neurosecretory centres in the central nervous system. The sinus gland is an important part of an elaborate neurosecretory system in the eyestalk of stalk‐eyed crustaceans and in the head of sessile‐eyed forms. It is largely composed of the swollen terminations of neurosecretory fibres. Some cellular elements have also been detected, but it is not yet known whether they have a secretory function. It is generally accepted that the greater part of the secretory material in the sinus gland has been transported thither along axon fibres from cell bodies in the central nervous system, though it has been suggested that the staining reactions of the sinus gland indicate also the probability of chemical transformation, if not autochthonous secretion. After‐sinus gland ablation the cut stump of the nerve leading to it continues to accumulate secretory material. An indiscriminate use of the term X organ in the eyestalk has led to confusion. The X organ, originally described in detail by Hanstrom, is characterized by its association with a sensory papilla and by its contained concentric‐layered structures, here called ‘onion bodies’. The term X organ has been used by some authors to denote a group of neurosecretory cell bodies, the fibres of which terminate in the sinus gland. It is suggested that the sensory papilla X organ (Hanstrom's X organ) should be distinguished from the other X organs as it differs from them morphologically and physiologically. The post‐commissure organs comprise enlargements of the epineurium of two post‐commissure nerves, containing the terminations of neurosecretory fibres. They have been shown to contain chromactivating hormones. The pericardial organs comprise epineurial enlargements containing fine‐fibre terminations. They lie in the pericardial spaces and have been shown to contain substances active on the heart. The Y organ, a glandular structure which contains hormones affecting the rate of development, is located in the antennary segment of those forms which have a maxillary excretory organ and in the second maxillary segment of those which have an antennary excretory organ. Various groups of neurosecretory cells have been detected in the brain and in thoracic ganglia. The term neurohaemal organ has been proposed to denote those tissues, through which substances produced in neurosecretory cells gain ready access to the blood. The pigment pattern of any one crustacean species is fairly constant, but patterns differ in the different groups. The pigments are contained in monochromatic, dichromatic, trichromatic and tetrachromatic chromatophores. The chromactivating substances which have so far been separated from tissue extracts seem to act differentially on these chr...

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