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Pacific flatfish from NorUi American and Japanese coastal waters regvilarly manifest skin tumours. Those are generally papillomas, which develop from primary inflammatory nodules (vascularized nodules) on fish of a few nionths's age. Inside the epidermal part of the tumour slightly dedifferentiated malpighian cells change to rounded enlarged cells showing evidence of considerahle degeneration (vacuolization and destruction of the cell oi'ganelles). These 'X-cells', wliich compose the major part of the mature tumour, always remain characteristically separated from the surface, from the hasal lamina, and from each other, by nonenlarged 'enyelope cells'.Oval, similarly degenerate cells also occur in the tumour stroma, especially in the nodule-like pre-papillomatous stages and here they originate apparently from fibroblasts.In the Atlantic, on the other hand, skin papillomas and other neoplastic skin growths occur relatively infrequently. The skin papillomas of Atlantic flatfish are considerably less complex. They belong to the relatively simple type wliich predominates in fishes in general-hyperplastic epidermal papillae which are supported and nin'tured by branched folds of the dermal tissue (stroma).Considering the close relationshi]) between the Pacific and Atlantic flatfishes, the distinctive structure of the skin tumours of Pacific lish is considered to be due probably to the influence of a specific virus.Introdviction odular or papillomatous neoplasia of the skin has been described in at least seven species of flatfish from the North American West coast. Previous investigations have concentrated primarily on three species; Parophrys vetulus Girard, Hippoglossoides

There are six transverse bands of sensory organs on the dorsal part of the labium of the water bug Cenocorixa bifida. Though phase contrast microscopy of the intact labium shows that each of these bands is made up of from four to six rows of sensilla, among which there are clearly several types of end structure, all appear to have the same ultrastructure below the surface of the cuticle.It was found by electron microscopy that each sense organ is composed of a single bipolar neuron, which, together with its sheath cell, forms a sensory unit. The dendrite of the neuron has a root system, two basal bodies, and an axial filament complex. It runs through the cuticle to the peg at the surface. Owing to difficulty in sectioning, no details of the terminal pegs were obtained, though they have a definite lumen at their base.The tips of the largest sensilla, but no others, were permeable to a solution of crystal violet. This permeability, their ultrastructure, and their location near the mouth and close to numerous obvious mechanoreceptors with long bristles, make it possible that these organs are chemoreceptors. Only electrophysiological studies can confirm this. The function of the rest of the sensilla, which form the majority, is unknown.

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