PHYSIOLOGICAL 259 



BIOLOGY OF THE TONGUE.— It is an ambitious task for 

 the tongue to tell the story of its own evolution. For there must have 

 been an evolution, since the first tongues (in fishes) were non-mobile, 

 and there were many millions of years before there was any tongue at 

 all. We must not, of course, mix up the tongue with the vocal cords, 

 which are the voice-producing structures, but as the tongue has 

 often had its share in modifying sounds, it is not irrelevant to think 

 for a moment of the ages in which there was no sound of life upon 

 the earth. There were cosmic sounds of wind and wave, of thunder 

 and cataract, but no voice of life. The age-long silence, as far as 

 living creatures were concerned, was probably first broken by the 

 instrumental sounds of insects like crickets and grasshoppers, pro- 

 duced by rubbing one part of the body against the other; but the 

 first true voice was in all likelihood that of pioneer Amphibians 

 that emerged towards the end of the Old Red Sandstone Age. 

 Nowadays, at any rate. Amphibians are the lowest animals to show 

 vocal cords and to utter controlled soimds, and it is interesting to 

 note that they are also the first animals to show a movable tongue. 



Many fishes have a tongue, and it is easy to see a cod's in the 

 fishmonger's window; but the tongue in fishes is non-mobile, without 

 intrinsic muscles. The so-called "tongue" of lampreys and hags, 

 which is used to work the boring apparatus and is very muscular, 

 must be excluded from the series, for it is not homologous with other 

 tongues. In fishes the tongue is a sensory organ, for touch and taste, 

 and in some cases, since it bears teeth, it probably serves to grip 

 the food before swallowing. Of course it can be moved as a whole 

 when the floor of the mouth is raised, but it cannot move of itself, 

 so to speak. 



Almost the same state of affairs is seen in some of the newts, 

 where the tongue cannot be moved ; and in some other Amphibians, 

 like the Surinam Toad and the Clawed Toads, the tongue is absent 

 altogether. We turn to the common frog, however, and we find a 

 tongue very highly developed. It is fixed in front and loose behind, 

 the very opposite of our own, and being well provided with intrinsic 

 muscles it can be jerked out to a considerable distance on an unsus- 

 pecting insect. Moreover, a large glandular region, that the fish does 

 not show, has been differentiated, and this produces a sticky secre- 

 tion very useful in insect-catching. The frog's tongue is folded back 

 on the floor of the mouth and has a broad, slightly forked, free end, 

 which is farthest in when at rest, but farthest out when the catapult 

 has been discharged. A very interesting little point is that the 

 tongue of the tadpole is at first so slightly muscular that it cannot 

 move itself. It is believed, however, that the included muscle-fibres 

 are of some primary service in compressing the tongue-glands. 

 Gradually they become stronger and able to move the yoimg frog's 

 tongue. Thus individual development recapitulates racial evolution. 



