OCR Text |
Show 320 DR. H. GADOW ON THE SPECIES OF RHEA. [Mar. 17, Tegumentary System. Concerning the coloration of the plumage, Rh. macrorhyncha is said to be distinguishable from Rh. americana "by its generally browner colouring, and by the darker crown, which is nearly black " (Forbes). Rh. darwini is characterized by its white-tipped feathers. How far these differences are subject to individual variation, and to age, is not yet satisfactorily known, owing to the scarcity of adult specimens of Rh. macrorhyncha. One decidedly good distinguishing character is given by the scales and the scutellation of the metatarsus. In Rh. darwini the distal half of the front side of the metatarsus is covered by broad transverse scutes, numbering about 20 ; whilst on the proximal half, the sides, and the hinder aspect of this portion of the foot the featherless inte- Fig. 11. Median view of the left foot of Rh. darwini, diagrammatic. The outer or fourth toe is not shown. gument is reticulated. The multangular reticulate little scutes are thickest and largest on the " heel," and are gradually decreasing in size towards the toes. The anterior dorsal surface of the toes is protected as follows :-The middle (3rd) toe is covered by 23 transverse broad scutes, which form the direct continuation of those of the metatarsus. The inner (2nd) toe possesses only about 9-10, the outer (4th) toe about 12 such scutes; these are biggest near the claws or nails, and gradually change into the reticulated structure which covers the first phalanx of the inner and outer toes. In Rh. americana and Rh. macrorhyncha the front of the metatarsus is covered with broad transverse scutes throughout its length, like the dorsal sides of the toes. Rh. darwini represents in this respect, like Dromaus and Casuarius, a lower stage than either Struthio or the other Rheas, since for obvious reasons the formation of broad scutes began distally, at the toes, and worked its way proximally upwards. Geographical Distribution. The geographical distribution of the three species of Rhea known at present seems to be the following:- Rh. americana ranges from Bolivia and the Province of Mattoo-rosso |