Then, those large eyes, with that capacity for reflecting light, are common features of nocturnal things—witness the owl and the cat.
But, gradually, the truth dawned on me: that Man had not remained one species, but had differentiated into two distinct animals: that my graceful children of the Upper-world were not the sole descendants of our generation, but that this bleached, obscene, nocturnal Thing, which had flashed before me, was also heir to all the ages.
There are no more uses of "nocturnal" in the book.
Show samples from other sources
The mice are nocturnal, so we never see them, but we see their droppings.