Slide showing a diagram concerning male and female genders and the codes P, F1, F2 and CLB. Slide shows a black and white diagram concerning male and female genders and the codes P, F1, F2 and CLB. There are three sets of diagrams in two columns, (female and male); the three rows are labelled 'P', 'F1' and 'F2'. There are two lines in each box, some are labelled CLB; some lines in the female column are connected to those in the male column by arrows. Late 19th to early 20th century