202 THE ZOOLOGIST. 



centre. The flexion of the toes is thus quite capable of provid- 

 ing sufficient lateral power to grasp small objects placed in the 

 extreme angle. It is easily tested in a dead bird, and freely used 

 by the Moorhen and its relatives when feeding on such sub- 

 stances as maize. Sometimes the hallux is used as a supple- 

 ment, but generally the grain is held tight either between 

 the second and third or the third and fourth digits. This is 

 by the way; I mention it because the point has escaped 

 notice, and the knowledge may be useful in a study of the 

 Grebes beneath water. 



Yet it often happens that a bird, from a position indicative of 

 extreme buoyancy, will on alarm sink in the water until only the 

 top of the back and the head and neck are visible, and this at 

 times when the aid of such things as plants is out of the ques- 

 tion. In fact, with the birds of the genus Colymbus, grasping is 

 anatomically impossible, even did the foothold exist. The Bed- 

 throated Diver, on occasion, swims as high in the water as a 

 Mallard ; yet when alarmed it will sink until almost all the 

 body is below the surface. This is true, to a certain extent, 

 of all swimming birds. Even the surface-feeding Ducks (as 

 Slaney noticed) are able to submerge their bodies to an extra- 

 ordinary extent. 



Without any further notice of facts that are common know- 

 ledge, an attempt can be made to solve the problem. It is merely 

 a question of specific gravity, and the methods by which this is 

 at the will of the bird. Gatke, in a well-known paper, attempted 

 to deal with the matter this way, but his essay was not a happy 

 one. For one thing, he guessed the bulk of a Great Northern 

 Diver to be about one cubic foot ! He knew the weight of a foot 

 of North Sea water to be sixty pounds, and a very little trouble 

 would have shown him that the bulk of a big Great Northern 

 Diver was not the third of a foot. 



I am enabled to give the exact bulk of a few typical water 

 birds. The cubic content of a Black-necked Grebe weighing ten 

 ounces was 25*3 in. — roughly speaking, the sixtieth part of a 

 foot. A Little Grebe of six ounces had a bulk of 13 in. ; a Smew 

 of fifteen ounces, 35 in. ; a Mallard of two pounds, 198 in. All 

 these calculations were made on clean dry birds, with the 

 " feather film " — to coin a convenient term — unbroken. Students 



