Here is how my mother sang it to me:

"Come, wife", said Good Old Farmer Gray,
"Put on your things, its market day.
"Let us be off and go to town,
"Returning ere the sun goes down.

"Spot knows we'll leave Old Spot behind."
And Spot, he barked and Spot, he whined.
He soon made up his doggy mind
To steal away under the wagon.
He soon made up his doggy mind
To steal away under the wagon.

They started off at a good round pace,
And joy came to the farmer's face.
"Old Spot", he said, "did want to come
"But I am glad he's left at home.

"He'll guard the barn and watch the cot*
"And keep the cows out of the lot."
"I'm not so sure of that", growled Spot,
The little dog under the wagon.
"I'm not so sure of that", growled Spot,
The little dog under the wagon.

The farmer, all his wares had sold,
And got his pay in yellow gold,
And so returning after dark,
Home through the lonely forest. Hark!

A tramp sprang out from behind a tree,
"Your gold or else your life", said he.
The moon shone bright but he did not see
The little dog under the wagon.
The moon shone bright but he did not see
The little dog under the wagon.

So Spot, he saved the farmer's life,
The farmer's gold, the farmer's wife,
And so a hero, grand and gay,
A silver collar he wears today.

And everywhere his master goes,
Among his friends, among his foes,
Spot follows upon his horny toes,
The little dog under the wagon.
Spot follows upon his horny toes,
The little dog under the wagon.

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Line breaks added --JoeClone