334 Frits Johansen. 



tail; only the eyes remain free and the animal is thus concealed. 

 The progression of the Apus along the bottom is marked by a cha- 

 racteristic, twisted tracing, which is formed by the feet whirling 

 the fine sand and mud away from the middle line of the belly, so 

 that a furrow is drawn across the bottom. The colour of the animal 

 is an excellent means of protection against enemies; it is grayish, 

 brown-yellow with small, dark points and spots, and in the water 

 it assumes a greenish shade quite like, for example, the moss plants. 

 Many a time I have lain by the banks and stared down into the 

 water, which was full of Apus, but it was only when they moved 

 that I observed them. They are found right in -on such shallow 

 water, that the carapace reaches the surface when they stand on 

 their heads in searching the mud. Sometimes we see them suddenly 

 mounting up through the water by means of active movements of 

 the tail and feet and swim for a long time, hanging on the surface 

 of the water with the ventral side uppermost and the tail down- 

 w^ards; the purpose of this is probably to provide themselves with 

 the food-stuff there (Infusoria etc.) or to imbibe air. It is curious 

 to notice how unwilling they are to lie on their backs; if they come 

 into this position by sliding down a stone or by the water suddenly 

 disturbing them, they set to work most strenuously with the tail 

 and continuous waving of the feet, so that there is scarcely a 

 single spot of the animal which is at rest — until they come right 

 side up again. Their food, which they mainly seek in the mud at 

 the bottom, consists of smaller animals; but that they may also 

 take free-swimming forms I found in July 1907 by keeping a number 

 of Daphnia piilex and Apus together in a glass with water; they 

 captured the Cladocera by movements of the body and feet, but it 

 was only when they had worked their prey up to the mouth that 

 they got a firm hold of it and ate it up. Their greediness was very 

 great and at last there was not a single Daphnia left, and as there 

 was no more food in the glass the Apus gradually died; which seems 

 to show that when they are free they must constantly have a supply 

 of food to be able to exist. That they may also be satisfied with 

 dead animals I observed on ^^/s 1907, when I saw the Apus tearing 

 up their dead comrades which lay on the bottom, so that only the 

 carapace remained. Regarding the possibilities of life for them out 

 of the water, I once observed numbers of small Apus by a bank, 

 consisting of a flat, gravelly beach, which had been washed up and 

 indicated the high water mark like a margin; they were all very 

 active and those highest up had already partly buried themselves 

 down into the moist mud. If the part of the lake where the Apus 

 live becomes dried up, one might believe the animals away, but on 



