Sentence:  The surest principle of classification is based on language, but the results must be tested by a study of the physical characteristics of the various races. According to this method of classification, the races of the world may be divided as follows: Aryan, Semitic, Hamitic, Turanian, Negroid. The name Caucasian is generally applied to the first three divisions, — <WSD>Aryans</WSD>, Semites, and Hamites. Aryan. — This includes the ancient Hindus ... the Persians, Greeks, Italians, Celts, Teutons, and Slavs. 
Meaning of the word marked with <WSD> tags:  A subdivision of the Caucasian racial and linguistic grouping, when that grouping is defined as consisting of Aryans, Semites, and Hamites.