608 MR, G. W. BUTLER ON THE [DeC. 3, 



generally. Thus, in the Snakes, Chelonia, Lizards, and Crocodiles, 

 there is a more or less marked tendency to the separation of the 

 .inner peritoneal or visceral layer of the body-wall from the rest, the 

 kidneys and fat-bodies being thus left more or less completely 

 outside the peritoneal cavity. 



On the other hand, Beddard's phrase (1, p. 105), — " the 

 horizontal membrane in Varanus, which shuts off both lungs from 

 the abdominal cavity," — together with the reference which 

 follows to the " membranous diaphragm " described by Martin 

 (P. Z. S. 1831, p. 138), indicates that it is used to include tissue 

 which shuts off the lungs from the peritoneal cavity. Here we have 

 a fact of considerable interest ; and neither the dissections nor the 

 transverse microscopic sections that I have made have rendered it 

 plain whether, as in birds, a pleural cavity originally exists, to be 

 subsequently obliterated by adhesions, or whetlier, as I believe to be 

 the case in Testudo, the lungs are not surrounded by any part of the 

 body-cavity. "Whichever be the case, the separation of the lungs by 

 a "membranous diaphragm " from the peritoneal cavity which con- 

 tains the liver and intestines is a feature that, so far as I know, is not 

 found in any other Lizard. But, on the other hand, the lungs and 

 liver are not thus separated in the Crocodiles either {cf. my paper 

 "On the Subdivision of the Body-cavity &c.," § v. this vol.). 



The preceding pages will show that in my opinion the Monitors 

 bear no special resemblance to the Crocodiles, so far as the relations 

 of the fat-bodies and the spaces and membranes about them are 

 concerned. The shutting off of the lungs from the liver, while sug- 

 gesting the condition in the birds, distinguishes them from the 

 Crocodiles, and, in the absence of developmental data, it may be 

 perhaps just as well explained by a reference to Testudo^. 



Again, seeing that some striking differences exist as to the sub- 

 division of the body-cavity in the other Lizards {cf. the case of the 

 Teiidee above, Plate XLVIIL and text, p. 466), it appears to me 

 doubtful whether, in our ignorance of the developmental history, the 

 shutting off of the lungs from the peritoneal cavity in the Varanidae 

 has much or little significance for the systematist. 



IIL Subperitoneal, Fat of Mammals. 



To turn to animals outside the Sauropsida, we find among 

 mammals deposits of fat on either side of the bladder (e. g. Kitten, 

 Guinea-pig, Hedgehog, young Kangaroo). It is impossible in some 

 cases to definitely mark off the fat in this position from that which 

 passes forwards on the dorsal side to the kidneys ; and both are 

 supplied by branches from the femoral artery (Guinea-pig). If this 

 vessel is the homologue of the femoral artery of Sauropsida, which 

 supplies the fat-bodies (Lizards) — seeing that in Lizards, Crocodiles, 



^ Emys, in which the lungs only partly project into the body-cavitj', would 

 seem to stand as a link between Tcsfiido and the majority of animals that have 

 the lungs fully projecting into the coelom, and to show that even such a striking 

 feature as the exclusion of the lungs from the body-cavity may be of comparatively 

 little systematic importance. 



