462 
dence goes to gain the verdict that the extirpation of the species (Alea tmpennis) was 
the work of man. 
Assuming a secondary law of the origin of species, the conditions of the characters of 
Alca impennis are explicable on the Lamarckian hypothesis of the *‘ modus operandi 
of such law, Rejecting a secondary cause in favour of a primary one, the original pair 
of Alca impennis were miraculously made in close conformity with the type of Alca 
forda, but with wings too small for the body and too feeble for effecting flight, such 
disproportion being the condition, on a coming event, of the destruction of the species. 
In the same view is added to the ‘ Appendix’ of the present work a brief notice of 
two species of terrestrial birds which, like Dinornis, have become extinct within the 
historical period, viz., the Dodo of the Island of Mauritius, and the Solitaire of the 
Island of Rodriguez. It will be helpful in the present speculation to determine how far 
the conditions of existence and of extinction of these wingless birds resemble those of 
the analogous species in New Zealand. 
Both Didus and Pezophaps surpassed in size the existing species of birds to which 
they bore the nearest affinity. ach genus was restricted, like Dinornis, to a limited 
tract of land. No evidences have been discovered in either Mauritius or Rodriguez of 
contemporary predatory animals, from the assaults of which a large bird would be 
impelled to escape by a rapid flight. 
Each of these richly wooded tropical islands affords abundant subsistence to vegetarian 
and omnivorous birds, and each, prior to the advent of geographical discoverers, was 
destitute of creatures able or desirous to destroy such birds. If the food was wholly, 
or chiefly, on the surface, the power of traversing such surface would be of as much 
adyantage to the bird as to the herbivorous quadruped, As flight calls for more effort 
than course, so cursorial progression would be more commonly practised in such happy 
islands for obtaining the daily food. The advent or proximity of a known element of 
danger might excite the quicker mode of motion; the bird would then betake itself by 
a hurried flight to a safer locality. If, however, these insular birds had never known 
a foe, the stimulus to the use of the wings would be wanting in species needing only 
to traverse the ground in quest of food. In the case of New Zealand, for example, 
the roots of wide-spread ferns, rich in farinaceous and amylaceous principles, tempting 
the birds to pluck, would stimulate such development of bone and muscle of the neck 
as is noted in pp. 407-420; or, if greater force was needed for the uprooting, the habit 
of scratching the food out of the ground would lead to excessive development of the 
muscles of the leg and foot. So such daily habitual exercise of legs and feet by 
unscared Rasorials would lead in successive generations to such developments of hind 
limbs as the Dodo and Solitaire present. 
We recognize in the stunted wings of the Dodo, as in the skull and the rest of the 
skeleton, evidences of its affinity to the Dove family (Coluwmbacei or Gemitores). The 
framework of the anterior limbs conforms, save in size and in the prominence of the 
