Carefully examined by the aid of a microscope, this tongue will be found to be made up of two separate tubes lying side by side, and, as each tube is grooved along its inner side, it follows that when the two separate halves are brought together, a third tube lying between the two outer ones is formed. So closely do these two halves fit when closed that this middle tube is perfectly air-tight. This union is secured by a number of hairy projections which interlock, much as one's clasped fingers interlock. Only the middle tube is used for the passage of the honey, the side tubes being used, as some think, for breathing purposes, while others hold that they serve to help in pumping up the fluids into the mouth. By this interlocking contrivance the tube can easily be opened and cleaned, should the passage become blocked by solid particles.
Delicate as this wonderful 'tongue' appears to be, it is in some cases capable of inflicting wounds on the tissues of the food plants. A species of moth, for instance, causes considerable damage to crops of oranges by inserting its trunk through the peel so as to suck the juices of the enclosed pulp. The sucking action is performed by means of a small bag inside the head, the size of which can be alternately increased and decreased by the action of muscles, thus causing a pumping action.
Fig. B.—Fly's Tongue (greatly magnified).
It will probably surprise many readers of Chatterbox to learn that this wonderful tongue is by no means always found in butterflies, for there are many species which have no mouth, and take no food whatever after they emerge from the chrysalis stage. They simply live long enough to lay their eggs, and then die!
Fig. C.—Common Fly.
The tongue of the fly is every bit as wonderful as that of the butterfly. Strictly speaking, perhaps it ought not to be called either a tongue or a proboscis, for it is really a spout-like mouth bent upon itself, and furnished at its end with a curious pair of flaps or lobes. You may get an idea of what it is like if you imagine the spout of a teapot to turn downwards at first instead of upwards, and then picture the spout turned sharply forwards near its middle. The body of the teapot corresponds to the fly's head; the end of the spout would correspond to the mouth of the fly. On each side of this mouth there will be found in the fly a pair of ear-shaped flaps or lobes, and these play a very important part. Each flap or lobe (see fig. [b]), where it joins the mouth, contains a long tube, and this tube gives off, along its outer side, about thirty smaller tubes, which are open below. Now, when the 'tongue,' as it is called, is extended, as in feeding, a copious flow of saliva is sent down the long tubular mouth into the tube of each flap, and when this is full the liquid escapes into the smaller tubes, and as these are open below, it flows out, of course, on to the food. Let us imagine this to be sugar. The saliva meets the sugar, and the syrup which is of course formed is then drawn up along the same channel as that by which the saliva came down. New surfaces for the saliva to work upon are constantly exposed by means of some fifty or sixty exceedingly tiny 'teeth,' which, by the aid of the microscope, will be found at the opening of the mouth, just where the tube-bearing flaps join it. The two rod-shaped, hairy organs at the base of the 'tongue,' in the illustration, are organs of touch, and not part of the 'tongue' proper.