Through October 25, Canadian auction house Heffel is hosting an online auction that features artwork by some of the world's major modern masters. The collection of international pop art and graphics ranges from the early 20th century to present and includes lots like iconic prints from Andy Warhol and Marc Chagall's color lithographs. Here are our highlights from the sale:

Pine Barrens Tree frog is a print from Andy Warhol's Endangered Species series. Using his signature style of blowing up subjects to fill the print and using bold neon colors, Pine Barrens Tree Frog was crated to draw awareness to the rare species. The dramatic red, green and orange frog set against the textured purple bark with its wide eyes fixed on the viewer makes this a compelling piece with an environmental message.

Three other Andy Warhol prints are part of this auction: Geronimo, Jean Cocteau and Wayne Gretzky.

The abstract work Le Dandy depicts a thickly rendered black figure, starkly set against a pale orange background that is splotched with bright colors. Joan Miró's use of aquatint make the background seem transparent and the central black subject anchors the work, yet its curved shape expresses a sense of movement and fluidity.

Untitled, Jasper Johns, lithograph

Untitled, Jasper Johns. Courtesy Heffel

Jasper Johns is one of the most celebrated modern artists, and his iconic paintings and prints led the New York Times to deem him "the foremost living artist" this year. Untitled is one of his lithographs that illustrates his signature integration of block lettering and numbers, stenciling and contrasting colors.

This 1980 lithograph is classic Marc Chagall, a whimsical and colorful scene that draws the viewer in with a flurry of activity. In Circus Parade, Chagall installs the recognizable circus figures (a grandstand audience, band musicians, animals jumping through hoops, gymnasts), but he also infuses an element of the absurd (a green horse leaps, a violinist stands atop an orange cow, an abstracted yellow-green bird peers in on the right edge) to create a pleasing, yet puzzling jumble that evokes circus entertainment.

Sonia Delaunay's fascination with color and geometric shape is on full display in this color etching, Untitled. She uses the lush shades of coral, sea green, cerulean and light crimson set next to varying gradients of black. This work is representative of the Orphism movement that Delaunay founded with her husband Robert that imbued Cubist-style works with vivid hues.