NINTH ANNUAL REPORT. 225 



thus homologous with that in Archaeopteryx. In an Ostrich, 

 which I observed closely, and which was almost denuded of 

 plumag-e, I again and again saw a curious and unexpected func- 

 tioning of the large second claw. This bird would frequently 

 flex the wing at the wrist and elbow, to an extent impossible in 

 an ordinary bird of flight, and vigorously scratch its side, and 

 even its neck. Ordinarily an Ostrich uses its toe in performing 

 the latter action. It was most interesting to see such an unavian, 

 ciuadrupedal act being performed by a bird. 



All the toes of struthious birds are provided with claws — the 

 four toes in the Apteryx, three in the Emeu and two in the 

 Ostrich. Although almost every text-book of zoology assures 

 us that the smaller toe of the latter bird is clawless, yet a claw 

 is often present, reduced, however, to about the size of the claw 

 on the foot of a common fowl. The short, thick, hoof-like char- 

 acter of the claw on the great middle toe of Struthio is an inter- 

 esting parallelism to the hoof of the perissodactyl mammals. 



An adaptation for defence is found in the claw of the inner 

 toe of the Cassowary. The other claws are of normal size, but 

 this one is very stout, sharp, and about four inches in length, a 

 weapon with which the bird can do terrible execution upon an 

 enemy at close quarters. 



Little of adaptative interest attaches to the scalation of the leg. 

 Although the entire hind limb of the Ostrich is bare of feathers, 

 yet this can hardly be explained as due to the increase of function 

 of that organ; for in one species of Rhea (Rhea darzvini), the 

 feathering is continued for some distance down, even on the tarso- 

 metatarsus. The pink coloring of the bare skin and leg scales 

 of some male Ostriches, differing in the dift'erent species, seems 

 to partake of the nature of a secondary sexual character. 



II. GENERAL FORM. 



A terrestrial life has had two diverse effects upon the eyes of 

 the ratite birds, throwing these organs into two very unequal 

 classes ; first, the eyes of the Apteryx, and second, those of other 

 members of the Subclass, of which the Ostrich may stand as an 

 example. Nocturnal habits, and a diet of earth-worms, as ex- 

 plained in Part I., have, in the Apteryx, resulted in the develop- 

 ment of the olfactory and tactile senses at the expense of the optic 

 power. In the Ostrich, on the contrary, the need for ptnverful 

 vision in detecting enemies upon the open desert, while they are 

 vet at a distance, has brought ab<nit a remarkably strong develop- 



