The metaphor of the animal frame
An animal frame is metaphorically used to refer to animal tendencies. One of the vital tendencies of animals, just like humans, is sleeping at night. Sleeping is an essential part of the animal kingdom. Sleep allows animals to rest after a long day's hunting work. After maximum rest, animals are energized to remain active for the entire day. The writer says:
“Two points are manifest: first, that the animal frame requires sleep, and a cessation of activity, which allows sleep being taken without interruption, and without loss.”
The metaphor of the constitution of animals
Under normal circumstances, a constitution is either a written or oral document that state how people are governed. Simply, it involves set rules that guide people on how they must live. Similarly, the author has used the animal constitution to metaphorically refer to the rules under which animals operate. Different animal species have marked boundaries with different structures and hierarchies of leadership. The author writes:
"I mean that it is conformable to the frame and wants of their constitution, that nature, by the very disposition of her elements, has commanded, as it were, and imposed upon them, at moderate intervals, a general in the transmission of their toils, their occupations and pursuits"
A simile of bats
The author has used the simile to help the reader understand how the bats would look like in the event they found no food. Without food, the bats would look like months and flying insects. He writes:
“As one example out of a thousand; the bat, if it did not sleep through the winter, it must have starved, as the moths and flying insects upon which it feeds disappears”
The metaphor of the oviparous economy
To help the reader interpret the interrelationship among animals, insects, and plants, the author uses the metaphor of the oviparous economy. For instance, months and butterflies lay their eggs on cabbage from which they nourish to young ones. Similarly, animals feed in particular plants. Plants get oxygen from animals to make their food. For instance, the author writes:
"There is another case of oviparous economy, which is still less likely to be the effect of education that is even in the birds, moths, and butterflies, which deposit their eggs in the precise substance, that of cabbage for example, from which not the butterfly herself, but the caterpillar which is to issue from her egg, draws its appropriate food."
Animal existence is made of action and slumber
The author has used this phrase to imply that animals have two major activities in their existence, which is activity and sleep. Unlike human beings who can multitask, animals are programmed to hunt and sleep. The writer notes:
“Animals' existence is made up of action and slumber; nature has provided a season for each”
