may react to the take-cover movements of other members of the colony instead of directly to the source of the disturbance. As a rule females seem more timid than males. The nice discrimination between disturbances and responses must be an asset in the economy of this crab—allowing more time on the open ground for feeding.

In times of danger a frightened Helice crassa individual will scuttle into the nearest available burrow whether occupied or not. On one occasion, when sufficient time had elapsed for the crabs to get over their fright, I saw four individuals emerge from the same burrow mouth.

Hemiplax hirtipes, which moves to a large extent amongst submerged vegetation and is not as nakedly exposed as Helice crassa, can be approached much closer and with much less caution before it runs for cover. If, however, their burrows are too far away, Hemiplax hirtipes individuals will either try to conceal themselves by burying on the spot or show fight. The burying technique is effective only in soft mud or sand below the water level. The crab first pushes its body backwards into the sand then, with alternate flexure and extension of the posterior legs, covers itself with sand so that its location can be identified only by the agitation of sand particles where the two exhalent breathing currents emerge. Crabs kept submerged on sand in the laboratory spent a large part of their time buried in this way.

If the animal chooses to show fight, it first adopts the “Aufbaumieflex” attitude, but if the source of the disturbance draws closer, the crab stretches itself upwards or sideways to its fullest extent, extends its chelipeds with the pincers wide open. and seizes some part of the intruder. This display is mostly bluff, as such crabs cannot inflict much damage on any of then enemies and, if escape is still possible, they usually discard the engaged limb and make off at top speed.