Summary.1The development of the middle ear is described inEremitalpa, ElephantulusandEriculus.The structure inEremitalpais fundamentally more primitive and quite distinct from that seen inEriculus.2The interossicular joints are in some cases clearly incapable of movement.3Evidence is brought forward for the view that the manubrium mallei and the element of Spence represent the insertion and horizontal portions respectively of the reptilian extrastapes,