Ill VARIABILITY OF SPECIES IX A STATE OF XATURE 69 



" In some species of Shrews (Sorex) and in some field-mice 

 (Ar^^cola), the Eev. 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 

 Ar^'icola 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 sho"«Ti 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 Cer\Tis 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 gi^eatly. 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 

 niunber 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 only 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 vridth and height, the 

 cranial ridge was either single or double, either much or little 

 developed, and the zygomatic apertui'e varied considerably in 

 1 Froc. Zool. Soc, 1864, p. 6i. 



