Slide showing table demonstrating: 'Percentages of polydactlyous guinea-pigs'. Slide shows table demonstrating: 'Percentages of polydactlyous guinea-pigs'. Title of table: 'Table 2. Percentages of polydactlyous guinea-pigs'. The table has five columns and four rows. Column 1 is entitled 'Age of mother'. Columns 2-4 are labelled 'Line A' to 'Line D' respectively. The four rows are as follows: 1 '3-6 months', 2 '6-9 months', 3 '9-15 months' and 4 '15- months'. Title below image reads: 'Effects of heredity and environment on the frequency of polydactyl (extra toes) in 1,986 guinea pigs. After Wright.' Late 19th to early 20th century