Slide showing two diagrams of 'Patella'. Slide shows black and white diagrams of 'Trochospheres of Patella at different stages' labelled A and B. Title underneath image reads 'Fig. 608 - A and B, Trochospheres of Patella at different stages. In A are to be seen the circular blastopore and the two foot-elevations; in B the blastopore is drawn out, at the sides of it there are two mesoderm bands. (From Korschelt and Heider, after Patten)'. Late 19th - early 20th century