On certain points in the Visceral Anatomy of the Lacertilia, particnlarly of Monitor.

Abstract

Summary. The principal facts recorded in the present paper and the conclusions to which they lead are as follows:- 1 The Varanidte differ from other Lacertilia in two important particulars:–in (i.) the occasional complication of the cystic and hepatic ducts, which form a network, (ii.) the presence of a fold of peritoneum, reflected from the lining peritoneum of the abdominal cavity, which surrounds the abdominal viscera. 2 This fold of peritoneum has its exact counterpart in Croco-dilia and Aves, where, however, the subdivision of the ccelom into a number of separate cavities is carried on still further. 3 The Varanidse, therefore, alone (?) of existing Lacertilia show the first beginnings of the subdivision of the coelom, which reaches its extreme in the higher Sauropsida. 4 These facts necessitate the separation of the Varanidse from the true Lacertilia into a group equivalent to that of, e.y., Rhyneho-cephalia. 5 It is probable, as generally believed, that the Lacertilia more nearly represent the primitive Reptilian stock than any other Sauropsida. 6 The particular resemblance between the Varanidse and the Crocodilia renders it probable that some Reptilian type existed in early Mesozoic or late Palaeozoic times, which in manv points, especially those enumerated in (1), resembled the existing Varanidee. From this type originated the Crocodilia, Diuosauria, and A.ves.