OF GALLINACEOUS BIRDS AND TINAMOUS. 151 
In the simple structure of the bones of the face, and in the condition, permanently, 
of certain structures arising from the great skull-balk, the Lapwing (Vanellus) and its 
immediate allies the Plovers, Sandpipers, and others are not so much specialized and 
modified from the low, fundamental, struthious type amongst the land-birds, and the 
equally generalized condition of the Penguins amongst the water-birds, as the Gulls on one 
hand and the Thick-knees (Gidicnemus), the Bustards (Otis), and the Cranes (Grus) on 
the other. Still the elevation of a bird in the ornithic scale does not ‘‘ go on all fours ;” 
it oscillates, as it were, in asort of see-saw manner. For instance, the Pigeons are almost 
as typical ornithically as the Passerine birds and the Crows ; yet, in the normal genera 
of the ‘‘ Columbine,”’ the base of the skull and the pterygoids are scarcely more removed 
from the struthious type than they are in the Fowl and the Plover. In the Dodo, 
in the Didunculus, and in the Goura the pedicles of the embryonic skull-base become 
arrested in the course of their growth ; whilst the wings of these birds are far inferior 
to those of the typical Pigeons. The “ Ralline,” again, are inferior to the Fowl-tribe 
in general intelligence, and far below the Pigeons; and yet, in them the skull passes 
through a more perfect metamorphosis’. This is the more remarkable when we con- 
sider, not only the struthious folly of this low-brained group, but also the abortive 
condition of the wings and sternum in Brachypteryx and in Notornis. So low are these 
latter birds in this respect, that our great naturalist, Professor Owen, forgetting the 
salient characters of the struthious skull, has unaccountably confused the two groups— 
the Notornis and the Cassowary becoming almost amalgamated in his inward vision. 
And this leads me to speak of isomorphism, or imitative resemblance independent of 
near affinity. 
In tracing out the almost infinite varieties of the modifications of any one specific 
type of shelled Rhizopod, my friend Professor Rupert Jones and I found that like 
varieties of distinct species were much nearer in shape and appearance than unlike varieties 
of the same essential species. This had caused the most pitiable ravelling of the forms 
in systematic works,—the ‘‘ isomorphs ” being put together, and the varied conditions 
of one and the same specific type (from overgrowth or from arrest, from happy or from 
inimical habitats) being placed at, in some cases, the very opposite poles of the order to 
which they belonged. 
Now, in venturing to work out ornithic affinities, I find it necessary to beware of 
being misled by mere isomorphism, and of mistaking it for immediate or pure affinity. 
The two are, however, often intimately blended ; and this makes the task the more diffi- 
cult. Such an instance of ‘‘ isomorphism,” I think, we have in the likeness of the 
Porphyriine Rails to the Cassowaries. 
We cannot say that there is no affinity ; there is such an affinity as must of necessity 
‘ One great difficulty in the derivative study of birds arises from the fact that in the Ostriches we have a 
blending of reptilian with mammalian characters: in the Penguin and the Cormorant the want of typical purity 
seems to arise from reptilian qualities merely. 
VOL, V.—PART III. x 
