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Show 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 whether, 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 contains 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 m y paper "On the Subdivision of the Body-cavity &c," § v. this vol.). The preceding pages will show that in m y 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 suggesting 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 Testudo1. Again, seeing that some striking differences exist as to the subdivision of the body-cavity in the other Lizards (cf. the case of the Teiidae above, Plate XLVIII. 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 Varanidse has much or little significance for the systematise III. 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, 1 Emys, in which the lungs only partly project into tbe body-cavity, would seem to stand as a link between Testudo 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 tbe body-cavity m a y be of comparatively little systematic importance. |