in VARIABILITY OF SPECIES IN A STATE OF NATURE 69 
“In some species of Shrews (Sorex) and in some field-mice 
(Arvicola), the lvev. L. Jenyns (Ann. Nat. Hist., vol. vii. pp. 267, 
272) found the proportional length of the intestinal canal to 
vary considerably. He found the same variability in the 
number of the caudal vertebrae. In three specimens of an 
Arvicola he found the gall-bladder having a very different 
degree of development, and there is reason to believe it is 
sometimes absent. Professor Owen has shown that this is 
the case with the gall-bladder of the giraffe.” 
Dr. Crisp ( Proc. Zool. Soc., 1862, p. 137) found the gall¬ 
bladder present in some specimens of Cervus superciliaris while 
absent in others ; and he found it to be absent in three 
giraffes which he dissected. A double gall-bladder was 
found in a sheep, and in a small mammal preserved in the 
Hunterian Museum there are three distinct gall-bladders. 
The length of the alimentary canal varies greatly. In three 
adult giraffes described by Professor Owen it was from 124 to 
136 feet long; one dissected in France had this canal 211 
feet long; while Dr. Crisp measured one of the extraordinary 
length of 254 feet, and similar variations are recorded in 
other animals. 1 
The number of ribs varies in many animals. Mr. St. George 
Mivart says: “ In the highest forms of the Primates, the 
number of true ribs is seven, but in Hylobates there are some¬ 
times eight pairs. In Semnopithecus and Colobus there are 
generally seven, but sometimes eight pairs of true ribs. In 
the Cebidse there are generally seven or eight pairs, but in 
Ateles sometimes nine” (Proc. Zool. Soc., 1865, p. 568). In 
the same paper it is stated that the number of dorsal vertebrae 
in man is normally twelve, very rarely thirteen. In the 
Chimpanzee there are normally thirteen dorsal vertebrae, but 
occasionally there are fourteen or oidy twelve. 
Variations in the Skull. 
Among the nine adult male Orang-utans, collected by 
myself in Borneo, the skulls differed remarkably in size and 
proportions. The orbits varied in width and height, the 
cranial ridge was either single or double, either much or little 
developed, and the zygomatic aperture varied considerably in 
1 Proc. Zool. Soc., 1864, p. 64. 
