478 MR. G. W. BUTLER ON THE [JunC 14, 



§ I. Introductory. 



This paper is a continuation of my previous one " On the Sub- 

 division 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 my investigations. 



1 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 my former teacher Prof. G. B. Howes, of 

 the Royal College of Science, South Kensington, who generously 

 placed at my 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 my specimens. 



§ IL Bibliography. 



The writer in Bronn's ' Klassen u. Ordnungen 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 Meckel ^ 

 downwards). But this is only one point about the peritoneum of 

 Snakes, and not 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 



' Deutsches Arehiv fiir die Physiologie (Halle), Band iii. 1817, p. 219. 



