Procure the placenta of a calf when it is born and observe the form of the cotyledons, if their cotyledons are male or female.
819.
Describe the tongue of the woodpecker and the jaw of the crocodile.
820.
Of the flight of the 4th kind of butterflies that consume winged ants. Of the three principal positions of the wings of birds in downward flight.
[Footnote: A passing allusion is all I can here permit myself to Leonardo's elaborate researches into the flight of birds. Compare the observations on this subject in the Introduction to section XVIII and in the Bibliography of Manuscripts at the end of the work.]
821.
Of the way in which the tail of a fish acts in propelling the fish; as in the eel, snake and leech.
[Footnote: A sketch of a fish, swimming upwards is in the original, inserted above this text.—Compare No. 1114.]
Comparative study of the structure of bones and of the action of muscles (822-826).