738 SUMMABY OF OUERENT EE8E ARCHES EELATING TO 



attributed to the molecular action between solid and liquid bodies; 

 or, in otter words, to capillary adhesion. 



If we examine the under part of the pulvilli with a Microscope, we 

 shall see distinctly that it is furnished with numerous hairs, regularly 

 distributed. These hairs terminate, at their lower end, in a kind of 

 bulb, the form of which varies, whence flows an oily liquid that dries 

 slowly and does not harden for a long time. The minute drops left 

 on the glass by the hairs may be taken away, even after two or three 

 days have passed, without our having to moisten them, by simply 

 rubbing a piece of fine paper over them. 



I have devised an apparatus for collecting these drops by cutting 

 a hole in a piece of board, over which I fix a glass slide. Turning 

 the board over so that the glass shall be at the bottom, I have a little 

 cell with a glass floor. With the aid of a piece of paper gummed 

 to the wings, I introduce a fly into this cavity in such a manner that 

 the pulvilli shall rest upon the floor. Then, putting the board under 

 the Microscope with the glass slide uppermost, we have the fly's feet 

 under our eyes. The insect, struggling for liberty, places his pulvilli 

 against the glass, and leaves after each effort traces that may be 

 observed very distinctly, for they are perfectly visible in a good 

 light. 



We may discover, whenever the feet of the fly come again in 

 contact with these tracks or minute drops, that they are composed of 

 a very liquid substance, for they spread quite readily on the glass. 

 We cannot admit, as some naturalists assume, that the liquid can hold 

 the club-shaped hair-ends by suction. If this were the case, the ends 

 would change shape during the suction, and would take the form of a 

 disk. The fly puts its feet down and lifts them up with an in- 

 comparable facility that would not exist if the limb were really acted 

 upon by the pressure of the air." 



Organs of Flight in the Hymenoptera.* — Dr. Amans has a further 

 paper on flying organs 'in insects, and in the groups now studied he 

 recognizes as constant factors the following. The general form of 

 the machine must be a more or less elongated oval, with its widest 

 end directed forwards. The framework must have a solid floor with 

 more or less elastic walls, more or less united behind so as to form a 

 fixed transverse pivot-line ; the walls must be sustained by a vertical 

 column, and there must be a roof movable on these walls around the 

 pivot-line, from before backwards and below upwards. The rotation 

 is effected by means of the wings. 



The " schematic form of the wing " is that of an elastic triangular 

 surface, the breadth of which gradually diminishes from before back- 

 wards, and from base to summit, the latter being centrifugal. For 

 its articulation the wing must have a double articular surface at its 

 point of attachment, and the movable roof must articulate with the 

 apex of the angle of the dihedron. The surface in front of the point 

 of attachment must be one of pronation, that behind it of supination. 

 The motors are (a) forces that are elevating, retracting, and divari- 



* Rev. Sci. Nat., xii. (1884) pp. 482-522 (2 pis.). 



