The Dutch scientist Jan Swammerdam did his dissertation in 1667 on “De respiratione” . On the engraved frontispiece we see two garden snails, their genitalia entwined. This behaviour was only noticed by a few years before by John Ray, who made observations in a Cambridge garden .
These snails seem two specimens of Cepaea nemoralis (Linnaeus, 1758), but likely from a Dutch garden, and quite realistically figured; both shells are dextral. The copulation is the first printed illustration of snail sex.
See also this blogpost  for notes on this engraving and the embedded reference system.
 Swammerdam, J. (1667). Tractatus Physico-Anatomico-Medicus De Respiratione Usuque Pulmonum: In Quo, Praeter Primam Respirationis in Foetu Inchoationem, Aëris Per Circulum Propulsio Statuminatur, Attractio Exploditur; Experimentaque Ad Explicandum Sanguinis in Corde Tam Auctum Quam Diminutum Motum in Medium Producuntur. Lugduni Batavorum: Apud Danielem, Abraham, & Adrian. à Gaasbeeck.
 Heppel, D. The long dawn of malacology: a brief history of malacology from the prehistory to the year 1800. Archives of Natural History 22: 301–319. See p. 309.
 http://inke-archbook.blogspot.nl/2012/01/notes-on-frontispiece-as-graphical.html (31.i.2014).