214 PEOF. W. K, PAEKEE OX THE 



well is i'eacly-j)repared to interpret the structure of all kinds of birds. Although less 

 modified than the fore limb, which has become a wing, the hind' Hmb is profoundly- 

 modified in birds — that might have been expected. The most remarkable fact, however, 

 with regard to the evolution of the amniotic Yertebrata, is that certain Reptilian types 

 (the Iguanodons and their allies) — forms that no possible development of A\"ings could ever 

 have Lifted a single inch from the Earth's surface — did, nevertheless, acquii*e a modifica- 

 tiou of the hind-quarters, quite similar to, and prophetic of, the hind-quarters of the 

 Bird. 



Remarkable as this coincidence certainly is, it helps us but little in our inquiry as to 

 the ancestral form of the Bird. Certain birds {e. (j. the Ostrich and its allies, recent and 

 recently extinct), by such overgrowth of their bodies as made flight impossible on this 

 planet, have been arrested as to the brain, and degraded as to the organs of flight. I 

 value the results of Palaeontology quite as highly as any of my fellow-workers ; but a 

 student of Development is the only worker who can let in any direct light upon this 

 subject. Every form with which the Palaeontologist amazes and delights us. had its own 

 developmental history : that cannot be traced, it can only be tentatively supplied by the 

 " scientific imagination " of one Avho is familiar with the development of living forms, 

 which yield us all the stages of then.' iransformation in their individual growth. 



We are still in the dark as to the relations of the Bird to the more archaic cold-blooded 

 Sauropsida ; it has not closely imitated any one of those old inhabitants of the land, the 

 marsh, and the water. 



That composite "monster," my 1st stage (Plate XXII. ), has not slavishly followed the 

 pattern of any one of the lost tribes ; its head is Ichthyosaurian, its spine Plesiosaurian, 

 and its hind-quarters Dinosaurian. But what of its chest and fore-quarters? It 

 certainly turns its small " thumb " inwards and upwards, as if to form a defensive spm", as 

 in IgvMiiodon bernissartensis (Dollo, Bull. Mus. Boy. Hist. Xat. Belg. t. ii. plate 5). 



Professor Huxley's " thi'ee-fold Law of Evolution " (Proc. Zool. Soc. 1880, pp. 649, 

 650) has mercilessly destroyed half the fore paw, and is beginning to melt together much 

 of that which is allowed to remain. Xevertheless, the partial destruction of the paw 

 will be the birth of the wing, such a wing as the cold-biooded Pterosauria lacked the 

 power to produce. This type, however, was grown in Nature's " hot-house ; " your 

 newly-hatched chick is as ripe a creature after three weeks' growth as the newly-hatched 

 Crocodile after three months and the Skate after six months ! Moreover, the Powl itself 

 belongs to the slow-growing forms that have precocious young ; it is one of the 

 " Prcecoces : " the " Altrices " develop very much faster, and are almost as large and as 

 active as their parents in four or five weeks after hatching, whilst in them the period 

 of incubation is greatly lessened ; they are, however, less mature at the time of hatching 

 than those which are rightly called Praecoces. 



At the end of one week's incubation the skeleton generally is marvellously perfect ; 

 the disproportion between the skull and the rest reminds one of the Tadpole. 



