270 Professor Owen on Metamorphosis and Metagenesis. 



which is converted into the hinder " horns" of the hyoid for 

 supporting the larynx. 



The scapular arch, which at first was connected with the 

 occiput, whilst supporting the branchial heart — its primary 

 function, begins as soon as the fore-legs bud out, to retro- 

 grade, and the sternum is developed to complete the point 

 d'appul for the fore-limbs. 



The food *of the larva is chiefly the soft decaying parts of 

 aquatic plants ; it has a horny beak, a long alimentary canal 

 disposed in a series of double spiral coils : but, as its frame 

 undergoes the changes adapting it for life on land, and a 

 purely animal diet, the mandibles are converted into jaws 

 and teeth, and the long spiral intestine into a short and 

 slightly convoluted one. 



Soon after the external gills have reached their full de- 

 velopment they begin to shrink and finally disappear ; but 

 the branchial circulation is maintained some time longer 

 upon internal gills : by anastomoses between the principal 

 branchial vessels these are converted into the aortic arches, 

 carotids and subclavians ; the internal gills with the cartila- 

 ginous hoops supporting them are absorbed, and lungs and 

 glottis for breathing the air directly are developed. 



Thus an animal formed for moving in water is changed 

 into one adapted for moving and leaping on land ; a water- 

 breather is converted into an air-breather ; a vegetable feeder 

 into a carnivorous animal : yet the series of transmutations 

 are limited to the nature of the species and produce no other. 

 The frogs that croak in our marshes are as strictly batrachian 

 as those that leapt in Pharaoh's chamber ; their metamor- 

 phoses have led to nothing higher than their original condi- 

 tion, as far as history gives us any knowledge of it. With 

 each successive generation the series of changes recommences 

 from the old point, and ends in a condition of the animal 

 adapted to set the same series again on foot. 



Having traced the principal stages in the metamorphosis 

 of an animal from a swimmer to a leaper ; the Lecturer next 

 took an instance where one that begins life as a burro wer or 

 a crawler is converted into an animal of rapid and powerful 

 flight. 



