828 
PEOPESSOE OWEN ON THE ISrEHATHEEIOI. 
and Glyptodon in South America; the fossil remains of ordinary Kangaroos and Wom- 
bats occur together with those of gigantic herbivorous Marsupials in Austraha; and 
there is similar evidence that the Apteryx coexisted with the Dinomis in Xew Zealand. 
I have been led, therefore, to offer the following suggestions as more applicable to, or 
explanatory of, the phenomena than Lamaeck’s progressive hypothesis of the origin of 
species by transmutation*, or Buffon’s retrograde hypothesis by degradationf. 
“ In proportion to the bulk of an animal is the difficulty of the contest which, as a 
living being, it has to maintain against the surrounding influences which are ever tending 
to dissolve the vital bond and subjugate the organized matter to the ordinai’y chemical 
and physical forces. Any changes, therefore, in the external circumstances in which a 
species may have been adapted to exist, will militate against that existence in probably 
a geometrical ratio to the bulk of such species. If a dry season be gradually prolonged, 
the large Mammal will suffer from the drought sooner than the small one ; if such 
alteration of climate affect the quantity of vegetable food, the bulky Herbivore will first 
feel the effect of the stinted nourishment ; if new enemies are introduced, the large and 
conspicuous quadruped or bird will fall a prey, whilst the smaller species might conceal 
themselves and escape. Smaller quadrupeds are usually more prohfic than largei ones. 
The actual presence, therefore, of small species of animals in countries where the larger 
species of the same natural families formerly existed, is not to be ascribed to any gradual 
diminution of the size of such larger animals, but is the result of cu'cumstances which 
may be illustrated by the fable of the ‘ oak and the reed ; the small animals have 
bent and accommodated themselves to changes under which the larger species have 
succumbed J.” 
Explanation of the Plates. 
PLATE XXXVII. 
Fig. 1. Side view of the pelvis: one-fifth the natural size. 
Fig. 2. The acetabulum. (By permission of the President and Council, from the speci- 
men presented by Sir W^oodbine Paeish, K.H., to the Museum, of the Royal 
College of Surgeons.) 
PLATE XXXVIII. 
Fig. 1. Back view of the left femur. 
Fig. 2. Back view of the left patella. 
One-third the natural size. 
* Philosopbie Zoologique, 8to. 1809, tom. i. ch. vii. 
t Histoire Naturelle, 4to. tom. iv. (1766), “Degeneration des Animans,” p. 311. 
J “ On the genus I>inornu” (part 4), Transactions of the Zoological Society, toI. iv. p. 15. 
