Siredon, breeding in the branchiferous stage, ii. [384].
Siskin, breeding in captivity, ii. [154].
Sivatherium, resemblance of the, to Niata cattle, i. 89.
Size, difference of, an obstacle to crossing, ii. [101].
Skin, and its appendages, homologous, ii. [325];
hereditary affections of the, ii. [79].
Skirving, R. S., on pigeons settling on trees in Egypt, i. 181.
Skull, characters of the, in breeds of dogs, i. 34;
in breeds of pigs, i. 71;
in rabbits, i. 116-120, 127;