PKOCEEDINGS OF SOCIETIES. 197 



tlie skull. His work had not direct reference to the subject of 

 teleology, nor to the structiu-e of the tissues ; but his object had been 

 to work out the metamorjijhosis of the skull, and to see the tissues as 

 they begin to differentiate and modify to form the embryo. The subject 

 was a very large one, and had been principally laboured at by the 

 great German embryologists. He had spent the last two years in 

 studying the development of the frog's skull, in watching the different 

 and numerous stages which that creature undergoes, and the relations 

 it bears to other creatures of the vertebrate type, always remembering 

 that the frog was essentially a fish. He had been in some degree un- 

 prepared for the extent of the metamorphic changes that the frog 

 underwent. He had worked out this subject into ten artificial stages, 

 the first of which he had obtained when the frog was in the egg. In 

 the first stage of its morphological development the animal was two 

 stages below the youngest described embryo of the lowest kind of fish, 

 but one. The larva of the lamprey was the earliest condition of a 

 fish's skull with which we are acquainted. He had succeeded in 

 getting two stages below the larva of the lamprey. From this stage 

 he had worked up the development of the frog until he came to the 

 tadpole, which is the representation of the types of rays and sharks. 

 As he ascended in the various stages the likeness to the other verte- 

 brata became very apparent. In an adult frog (Bana temporaria) he 

 had obtained a metamorphic development of such height that it 

 bordered upon our own class, the Mammalia. At the same time it 

 should he stated that other parts of that frog's skull retained the 

 simplicity of the adult lamprey. In the frog we had a creature who 

 had run across the whole circle of types, creeping gradually up to the 

 Manimalia, and yet never losing his relation to the original type, but 

 retaining its structure and relation to the very end, although sub- 

 dividing and metamorphosing certain of the facial arches into the 

 very number of parts that we have in our own inner ear. The 

 chain of bones in the human ear (the hammer, the anvil, the round 

 bone, and the stirrup) had caused a great deal of trouble to anato- 

 mists in their attempts to trace the series of metamorphic changes. 

 He^ had, however, made this clear by tracing the history of the 

 facial bones of a frog, a creature which was but a fish in respect 

 of its earliest embryonic conditions. Supposing the doctrine of 

 development to be true, it would seem that we ourselves have come 

 originally in some line sub-parallel to the frog (he would not say 

 from the frog itself, although man had repeated the form tail-less). 

 Even in the highest oviparous vertebrates no subdivision of a facial 

 bar to form that tiny but really important part of the human skull, 

 the OS orhicidare, ever obtained. In this respect the frog comes nearer 

 to the Mammalia than any bird. Birds have branched out in a direc- 

 tion quite away from the ordinary line, and have culminated in their 

 own glorious types. If it is desired to trace the development of the 

 Maniinalia, inquiries must commence with the Batrachia ; and in such 

 inquii-ies the thought constantly occurs that between us and the 

 Batrachia there have been lost whole groups of creatures. We were 

 only just beginning to see the manner in which the work of tracing 



