Illustrations have been moved alongside the text which they illustrate, and may no longer match the locations given in the List of Illustrations.

The following apparent errors have been corrected:

• p. vii "FIG" changed to "FIG."
• p. viii "Mr" changed to "Mr."
• p. 29 "Figs. 9" changed to "Fig. 9"
• p. 34 (note) "on" changed to "of"
• p. 50 (footnote) "p 88" changed to "p. 88"
• p. 72 (note) "(1898)" changed to "(1898)."
• p. 107 (note) "405" changed to "405."
• p. 131 "219" changed to "219."
• p. 131 (note) ">Pfluger’s" changed to "PflÜger’s"
• p. 162 (note) "p 44" changed to "p. 44"
• p. 165 "Mullerian" changed to "MÜllerian"
• p. 212 "Where-ever" changed to "Wherever"
• p. 216 "79" changed to "79."
• p. 226 "drives" changed to "drive"
• p. 239 (note) "G. F" changed to "G. F."
• p. 256 "objects" changed to "objects."
• p. 267 "woes" changed to "woos"
• p. 330 (note) "239" changed to "239."
• p. 332 "co ordinated" changed to "co-ordinated"
• p. 338 "106." changed to "106"
• p. 338 "Beckstein" changed to "Bechstein"
• p. 338 "leafcase" changed to "leaf-case"
• p. 339 "nerve centres" changed to "nerve-centres"
• p. 341 "nerve centres" changed to "nerve-centres"
• p. 341 "king crab" changed to "king-crab"
• p. 341 "of, intelligence" changed to "of intelligence"
• p. 342 "on, infusoria" changed to "on infusoria"
• p. 342 "mating, instinct" changed to "mating instinct"
• p. 343 "Schneider on" changed to "Schneider, on"
• p. 343 "Shock effects" changed to "Shock, effects"
• p. 343 "Spence on" changed to "Spence, on"
• p. 344 "106." changed to "106"
• p. 344 "of 327" changed to "of, 327"
• p. 344 "72 ff.," changed to "72 ff.;"

Punctuation and spelling have otherwise been kept as printed.

The following are used inconsistently in the text:

• alarm-note and alarm note
• co-existed and coexists
• co-incident and coincident
• danger-note and danger note
• first-hand and firsthand
• fox-terrier and fox terrier
• ground-work and groundwork
• inter-communication and intercommunication
• newly-hatched and newly hatched
• non-plussed and nonplussed
• play-time and playtime
• pre-requisite and prerequisite
• re-presentations and representations
• re-presentative and representative
• Romanes’s and Romanes’
• supra and supra
• Venus’s Fly-trap, Venus’s Fly Trap and Venus’s fly-trap