Much has been written about Cetology.
For example, there are some for whom Cetology is what it purports to be: a Cetological classification of whales based on a review of the literature and personal observation. See, for example, this discussion in Wikipedia, which neatly summarizes the Cetological classification among different books (e.g., Folio, Quarto, Duodecimal), and contrasts it to modern Cetology, which has over ninety categories of whales, far more than known by Ishmael.
Others, however, perceive the deeper import of Cetology. In CallmeIshmael, for example, a particularly melodic blog, we can see a reading of Cetology which focuses on the chapter's exceedingly random classifications of whales as a critique of racism and the random classification of people.
Yet others classify the chapter based on its relative length, and it is, of course, among the longest of chapters in Moby-Dick. These scholars often note Melville's painstaking efforts to do everything possible to accentuate the apparent length of the chapter, just as many an "usher"(*) knows how to make the most of the last five minutes of every hour.
Still others emphasize the role played by the knowledge imparted in this chapter and its utility in the narrative sections of the book, where the discussion frequently uses terms with some technical precision in the whaling industry. Confer, for example, Howard P. Vincent, The Trying-Out of Moby-Dick, p. 123.
Finally, there are those who view all cetological discussions, and all discussions on whaling in general, as "in essence metaphorical", comparing whales and in particular the whale to the condition of man. A fine example of this is found in J.A. Ward, once of Tulane University, in his "The Function of the Cetological Chapters in Moby-Dick", which first revealed this reading to a here-to-fore unsuspecting public in the May, 1956 issued of "American Literature".
I, however, would propose that we reject each of these approaches to Cetology, and instead focus simply on one small statement at the beginning of the chapter, where Ishmael tells us what he is doing:
It is some systematized exhibition of the whale in his broad genera, that I would now fain put before you. Yet is it no easy task. The classification of the constituents of a chaos, nothing less is here essayed.
Now, usually, I too would not look for answers to great questions in so plain a statement, but, in this case, I would ask that you just humor me. Ishmael describes the whales as "chaos"; could he perhaps mean that they are, indeed, chaos? Chaos is often used in two ways: a collection of disorderly things, or, alternatively, the unformed matter at the beginning of the universe.
If the whales are a collection of disorderly things, perhaps what Ishmael is doing is trying to make order of them, that is, trying to find way to make the chaos make sense to him. Perhaps this is why he classifies based on, for example, size and commercial utility. Under this use of chaos, I might suggest that the classification speaks not to us about the whale, but about the classifier.
With respect to the other definition of chaos, the disordered welter and waste at the beginning of the universe (above is a NASA image of the congealing of matter after the big bang), what can we say of it other than that it is even more unknowable than the God or natural force that ordered it? Is not this chaos, of mythological and scientific reknown, the most puzzling thing of all, and thus the task of putting order to it very much a fictional rather than scientific undertaking, one that relates more to the crafting of myths than the examination of things?
Perhaps, what Melville is trying to do here is show Ishmael doing both things, that is, not just classifying but ordering chaos; but that would put Ishmael, or perhaps Melville, at the treadle of the loom, which is too presumptuous to be believed.
This is all, of course, conjecture on my part. Luckily, Ishmael will examine whales from many perspectives, not just this cetological one, and, perhaps, when we explore these creatures, and the White one in particular, from all angles, and in all ways, we shall gain some knowledge, useful or not, of them.
* Note that the word "usher", as used in Melville's etymology, references a then-obsolete and now even more so use of the word to mean an assistant teacher in a lower school; note further that footnoting this provision through a cross-reference to an etymology does for my discourse much what Melville's thirteen pages did for his Cetology.