In Memoriam isn't so much a poem as a collection of poems; 131, of them, to be precise. (Or 133, if you include the prologue and epilogue). Each individual poem, or canto, is comprised of four four-line stanzas written in a regular meter—iambic tetrameter, with four iambic feet in every line—and with the rhyme scheme abba.

The structure of the poem is entirely intentional on Tennyson's part. The dividing up of the poem into cantos and the regularity of both the meter and the rhyme scheme combine to convey the impression that the speaker is in mourning and, what's more, is unable to move on from his grief. As each canto is self-contained, it does not flow naturally into the next one. It cannot move on very easily, just as the heartbroken speaker cannot move on from his terrible loss.

Some readers have found that the rigid structure of In Memoriam, coupled with the regular rhyme and meter, is rather monotonous, to say the least. Others, however, have been more charitable, seeing Tennyson's approach as being entirely appropriate to his theme.

Whichever view we might choose to adopt, there's no denying that it is common for the bereaved to seek some sort of stability in the midst of their overwhelming grief, and Tennyson is no different in this regard. Constructing his elegy to Hallam in the way that he does gives him some much-needed stability in his life at a time when his battered emotions are in a state of turmoil.