Professor Owen on Metamorphosis and Metagenesis. 269 



beings, and the supposed peculiarly animal and vegetable 

 characters taken singly, interdigitate, as it were, and cross 

 that debatable ground and low department of the common 

 organic world from which the specialised plants and animals 

 rise ; and there are numerous living beings with the common 

 organic characters that have not the distinctive combined 

 superadditions of either group. 



Between the organic and inorganic worlds the lihe of demar- 

 cation may be more definitely drawn. The term *' growth*' 

 cannot be used in the sam^ sense to signify the increase of a 

 mineral and of an organism. The mode of increase is dif- 

 ferent ; there is a definite limit to it in the organic kingdom, 

 and something more than mere growth takes place in the pro- 

 gress of an organism from its commencement to maturity. 

 This was exemplified by reference to the human subject, to the 

 lion which acquires its mane, to the stag which gets its horns, 

 and to the change of plumage in birds during the course of 

 growth. The changes of form and character are still more 

 remarkable in the kangaroo ; and in the frog they are such 

 as to have received the name of " metamorphosis.^* 



The development of the frog was traced to its exclusion 

 from the egg in the form of a fish, with external gills, a long 

 caudal fin, and without legs. 



The internal skeleton, like the external shape, is adapted 

 for aquatic life. 



Only those parts are ossified which are to be retained in 

 the mature state. The vertebrae are at first biconcave, as in 

 fishes, with intervening spherical elastic balls filled with fluid : 

 they are converted into ball and socket joints by the ossifica- 

 tion of the sphere, and its anchylosis to the back of the ver- 

 tebrae. The pelvis and hind legs are progressively developed ; 

 and, whilst this change is proceeding, the tail is undergoing 

 proportional absorption. The chief change in the skull of 

 the larva is operated in the lower or haemal arches and their 

 appendages. The maxillary arch is widened and provided 

 with teeth, and the horny mandibles are shed. The mandi- 

 bular arch retrogrades as well as expands. The hyoidean 

 undergoes a remarkable change of size and shape, and the 

 branchial arches are absorbed, excepting a small portion 



