All work and no play makes Virgil write Eclogues 10

When we were originally talking about word play and the differences between forests/woods/meadows in class, I also thought about the beginning of the poem. I thought it was funny that Virgil began his poem by addressing Arethusa, and how that reflected calling the Muses. I wondered if Virgil did it differently because he was not Greek, and only honoring the Greek invocation, but I noticed that Virgil is very selective in his writings. So, why is it different? It made me wonder about two things; 1). the proper way of calling a muse or The Muses - the Greek way, and 2). all the poems that do not call the muses in a "traditional" way, and why they are different (is it just because they are not Greek or is it something else?).

For a brief overview on the invocation of the Muses. The poet is the bringer of two worlds, the immortal realm and the mortal realm. They are basically the poet, the prophet, and the philosopher - and the only one who the gods bestow divine knowledge (Murray 1983). If the gods, or the Muses, choose you, or if you call to them, then the story can be told. Pindar, Homer, and Hesiod are well known to invoke the Muses at the very beginning of their poems. "Sing, O goddess, the anger of Achilles son of Peleus, that brought countless ills upon the Achaeans" (Perseus translation). 

Virgil writes;

Extremum hunc, Arethusa, mihi concede laborem 

"Here, at last Arethusa, yield to me the work."

Which I find kind of strange.

First, Arethusa is a nymph from Arcadia. I do not think she is the type that a poet would write an invocation to. She is a favored nymph of Artemis, however, and Virgil does mention Pan of Arcadia. Is this the reason for her call and connection?

Second, I wonder about his wording. "Laborem" seems to be a harsh word for a pastoral poem. To me, Virgil is saying that Arethusa give him the work of singing about Gallus properly, rather than asking her to give him the ability to sing about Gallus. 

Then, I wondered, if other non-Greek invocations were similar to Virgil? The only one I could think of was John Milton with "Paradise Lost." Although not the first line of the poem, Milton does write:

Sing Heav’nly Muse, that on the secret top
Of Oreb, or of Sinai, didst inspire That Shepherd...(Milton 1674, 1.6-8).

Unless I am wrong, that sounds like a proper invocation. So, why is Virgil asking for the laborem and not otium? (A question that was also proposed, and written about, by Lorina N. Quartarone in her 1996 dissertation entitled "Locus ambiguus: From 'otium' to 'labor' in Vergil's 'Eclogues' and 'Georgics'")

Although I do not have an answer, I can say that Arethusa had a lot on her plate if she had to write so many songs about Gallus while worrying about the river god, Alpheus!

Resources:

    The Iliad, Homer. Samuel Butler, Ed. (http://www.perseus.tufts.edu/hopper/text?                                doc=Perseus%3Atext%3A1999.01.0217)
    Paradise Lost, John Milton (1674)
    Quartarone, L. N. (1996). Locus ambiguus: From 'otium' to 'labor' in vergil's "eclogues" and "georgics." (Order No. 9716902, University of Washington).