text: 'Atlas d'Histoire Naturelle : Scènes de la Vie des Animaux' {A. Ract & Co. Editors} undated but say, 1875, is online via la Bibliothèque des Sciences et de l'Industrie (BSI) in Paris. [The portal: La Médiathèque à Paris au cœur de la Cité des Sciences et de l'Industrie]
  "Even though chromolithographs served many uses within society at the time, many were opposed to the idea of them because of their lack of authenticity. The new forms of art were sometimes tagged as "bad art" because of their deceptive qualities. Some also felt that it could not serve as a form of art at all since it was too mechanical, and that the true spirit of a painter could never be captured in a printed version of a work. Over time, chromos were made so cheaply that they could no longer be confused with original paintings. Since production costs were low, the fabrication of chromolithographs became more a business than the creation of art." [W]Neil from Idbury Prints informs me that the 'striped' appearance in many of the pictures is due to the quality of the digital photography. The illustrations were printed on laid paper which has an embedded striated pattern caused during the paper's unique production technique that is being recorded during digitisation. It would hardly be noticeable with the naked eye.
  There's a centuries-old illustrative style expressed in those quizzical stares you mention, as well as in the embellished renderings of the monkey faces. I'm not sure whether it's from a belief in the animals possessing souls like humans or if it's simply an artistic habit of portraying their subjects as having greater or more attractive character than they do in reality. (Occam's razor says it's about $$ and increased sales I suppose)It brings to mind - although not necessarily in the stares - a concept I see as the 'distance law of artistic absurdity' at play : the more obscure or exotic the animal (and thus the further away in distance from a book's publication city), the greater was the poetic license of absurdity in the drawing of the animals's characteristics. So we get apes with semi-human faces and animals staring back at the viewer as though finding us totally absorbing and interesting. It goes back to the manuscript days of course.