Note 186 — Chapter IX · THE ORDER UNGULATA

The stomach of the Camel inhabiting the Arabian desert is commonly looked upon as a striking example of specialised structure, adapted or modified in direct accordance with a highly specialised mode of life; it is therefore very remarkable to find an organ exactly similar, except in some unessential details, in the Llamas of the Peruvian Andes and the Guanacos of the Pampas. No hypothesis except that of a common origin will satisfactorily account for this, and, granting that this view is correct, it becomes extremely interesting to find for how long a time two genera may be isolated and yet retain such close similarities in parts which in other groups appear readily subject to adaptive modifications.