P.1 Santiago Cajal (1852–1934)
P.2 A hand-drawn diagram from Cajal’s (1894) publication showing the growth of a neuron (a–e) and contrasting neurons from frog (A), lizard (B), rat (C), and human (D) samples
P.3 The reading trilobite enjoys expanding your knowledge
P.4 This trilobite calls attention to tricky passages of text
1.1 The number of species on our planet began to increase rapidly 550 million years ago, during the prehistoric Cambrian period
1.2 A bespectacled trilobite
1.3 The Nobel Prize-winning neurophysiologists Torsten Wiesel (left) and David Hubel
1.4 Hubel and Wiesel used a light projector to present slides to anesthetized cats while they recorded the activity of neurons in the cats’ primary ...