First published in 1917; revised in 1942 - about 800 and 1100 pages respectively. Those volumes are collector's items by now and perhaps stand as a monument to disinterested curiosity in wartime. This edited Cambridge University version (editor John Tyler Bonner) is about 300 pages and therefore seriously shorter, though the original wording and diagrams were retained as much as possible.
For people unused to this type of material, let me list a few topics (examples only, and simplified!):--
[1] The properties of oxygen - its diffusion in liquids and so on - determine the maximum size of organisms which need oxygen for energy. (I.e. animals rather than plants). Thus insects - which have no heart - are smaller than mammals, for example. Partial pressures of oxygen and nitrogen dissolved in river water have their own controlling influences.
[2] Lengths, areas, and volumes when scaled up are in proportion to l: l squared: l cubed. Thus an internal skeleton, made twice as tall, must support about eight times the musculature of the original skeleton. This sort of thing helps explains thicker bones in large animals - and such things as lung size, and heartbeat rate.
[3] Fish are supported by the surrounding water, and are roughly as efficient irrespective of size. Birds on the other hand cannot fly if their wing size and muscle ratio are too small. Hence birds's sizes have evolved to be very accurately controlled, while fish may grow in size almost indefinitely.
[4] Because of diffraction at the side of a pinhole (i.e. blurring), very tiny eyes cannot have pupils.
[5] Ram's horns grow in a spiral, of a type with keeps the centre of gravity constant. Thus ram's heads bear their load in an efficient manner.
Fascinating stuff which needs some mathematical flair to grasp - though the flair needed is not so much arithmetical and a matter of counting, as geometrical and a matter of appreciation of physics. The material omitted is (I think) on less precise topics, such as water flow in tubes, and the formation of eddies and smoke.
I have one reservation: material on cell structure was edited out by Bonner on the grounds it's outdated. In fact there's overwhelming evidence now that much post-1945 biology of the cell is erroneous. Possibly in time a new comprehensively updated edition will be issued, though it would (probably?) be a work of love rather than profit.