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Show 478 MR. G. W. BUTLER O N T H E [June 14, § I. Introductory. This paper is a continuation of my previous one " On the Subdivision of the Body-cavity in Lizards, Crocodiles, and Birds" (Proc. Zool. Soc. 1889, p. 452). Probably most persons will admit that the comparative study of any structure is more or less useful, since any such study may at any time suggest or confirm relationships between different types, or may throw light on physiology. But whether there be much or little interest in the relations (in the different groups of the Amniota) of the pleuroperitoneal cavity, with its more or less complete subdivision into different spaces, by longitudinal, transverse, or oblique membranes or " diaphragms," the fact remains, that any departure from that which embryology shows to be the simplest arrangement (viz. that seen in Lizards) at once arrests the attention of the anatomist; and, accordingly, much is from time to time written on the subject. Therefore, as the matter is one which cannot be satisfactorily discussed except after somewhat laborious work in embryology and comparative anatomy, I have thought it well, having once gone some length in the matter, to continue m y investigations. I have to thank the " British Association," the occupation of whose "table" at the Zoological Station at Naples in 1890 gave me facilities for the collection of various Reptilian material, embryological and otherwise, and also m y former teacher Prof. G. B. Howes, of the Royal College of Science, South Kensington, who generously placed at m y disposal a large variety of Snakes, with permission to work at them in his laboratory. I am also indebted to Mr. G. A. Boulenger, who has kindly identified many of m y specimens. § II. Bibliography. The writer in Bronn's ' Klassen u. Ordnungeu des Thierreichs' (Band vi. Abth. 3, p. 1544) says:-" The peritoneum of the Python, and apparently of many exotic Snakes, exhibits peculiarities not known in any other vertebrates. These peculiarities have been often described, and always as something quite ' new ' "; and he goes on to give references. It would appear, however, from the way he speaks, and the references he gives, that the " peculiarities " of which he is thinking consist simply in the relation of the peritoneum to the stomach and intestine, the individual coils of which latter it does not follow. And, such being the case, he is quite right in saying that they have often been described (at any rate from Meckel1 downwards). But this is only one point about the peritoneum of Snakes, and nbt the most interesting one. While one of the authors to whom he refers us [namely Retzius, (1) & (2)] has noted all the other peculiarities, Duvernoy confines himself to the one point above mentioned, and Herring, who is quoted without adverse 1 Deutsches Archiv fur die Physiologie (Halle), Band iii. 1817, p. |