14 



THE ZOOLOGIST. 



stomachs of some waders killed on soft ground. It does not 

 appear to be an inconvenience to them, and the friction gene- 

 rated by the particles of sand and mud during the act of pre- 

 hension may help the birds to deal with the slippery animals 

 which are their food. 



When the supply of food is scanty the imprints are reduced 

 to a small number per square foot, and usually they are of 

 the deep kind, but have lost the typical form. This is due to 

 the Dunlins feeding by sight and touch together, when the 

 apparent tremor of the bill becomes more marked. The probings 

 are expanded irregularly. They may be elongated, wedge- 

 shaped, with the base directed downwards, or converted into 

 circular pits, and if they are opened gently the walls are seen to 

 be covered with numbers of nipple-shaped depressions. On the 

 level sands, where active Crustacea are the objective, we see 

 long lines of footmarks leading in every direction, and here and 

 there isolated deep probings, or lines of contiguous septate 

 probings, each line ending in a complete probing. Where it is 

 sandworms, we see in places a single deep probing in the most 

 recent part of a worm-casting, which is always small. 



I have tried probes made of various materials, but for delicacy 

 of touch none of them is equal to bone covered with soft skin. 

 When contact is made with a living animal a peculiar quivering 

 sensation is experienced, like that felt on touching a vibrating 

 chord. At the same time the animal, especially if it is a worm, 

 stiffens itself preparatory to making its escape. If it is a shell 

 it appears to rise up slightly and proceed slowly to close its 

 operculum or valves. This feeling can be obtained not only by 

 contact with the probe, but also, after a little practice, through a 

 quarter of an inch of intervening soil. It is, I imagine, a sensa- 

 tion like this that guides the Dunlin, in addition, of course, to 

 the disturbance of sand and mud which the animals make when 

 in motion, and it serves to distinguish living animals from 

 inanimate objects offering an equal degree of resistance* to 

 the bill. 



* Macgillivray, « History of British Birds,' iv. pp. 207- 213. 



