Slide showing three figures and text describing the 'crossing-over between two X chromosomes'. Slide shows three figures (Fig. 14 - Fig. 16) and text describing the 'crossing-over between two X chromosomes'. The text is as follows: 'That crossing-over betwee two X chromosomes takes place has been confirmed by examination of offspring of XX males. This is observed in two cases within the XX race, as showing in Fig. 14 and 15'. 'The genealogical table in Fig. 14 shows that a male Xo Xvi must have arisen through crossing-over from X to X in the father. In Fig. 15 the occurence of a male Xo Xco must like-wise be due to crossing-over between the two X chromosomes of the father, namely, in the manner illustrated in Fig. 16'. Late 19th to early 20th century