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Show 1892.] BODY-CAVITY IN SNAKES. 485 'Forms of Animal Life,' 2nd ed. p. 69). From my tabulated notes I find that the straight terminal portion of the intestine seldom projects at all into the body-cavity, and that the less folded portion, immediately preceding this, seldom (as in Ccelopeltis lacertina, Crotalus durissus, Compsosoma melanurum, and Python) has anything that can be called a mesentery. As to the zigzag part of the intestine that follows the stomach, the peritoneum (as so often noticed) does not follow the individual bends, but merely covers the zigzag as a whole. In fact the intestine of Snakes, as a rule, intrudes upon the peritoneal cavity less than in any other Vertebrates. Secondly, as to the kidneys l. With rare exceptions, the permanent kidneys in Sauropsida (unlike the Wolffian bodies of the embryo, and the kidneys of certain Mammalia) do not project freely into the body-cavity, but are in great part, if not entirely, situated outside it2. Snakes are no exception to this rule. In Boa constrictor, it is true, I have found the kidneys hanging freely in the body-cavity, as in certain Amphisbaenidse, but this is the only case I have found among Snakes. The only other Snakes in which I have found any part of the kidneys projecting into the body-cavity are Typhlops, Ccelopeltis, and the Pythonidce, and in these cases the intrusion is but slight. In all the other forms examined (see list § III.)3 the kidneys lie entirely outside the peritoneal cavity, and do not project at all into it. It is interesting to note that this exclusion of the kidneys from the body-cavity in Snakes is, like the absence of this •cavity round parts of the alimentary canal, not primary. That is to say, when, at a comparatively late embryonic stage, the permanent kidneys first begin to develop, they in part project into the peritoneal cavity, as is the case in the adults of some (and perhaps most) Lizards. Thirdly, the only other organs whose relations to this hinder peritoneal space we have to consider are the reproductive ones; and these in both sexes (and as I believe to be the case in all Vertebrates) project freely into the body-cavity. Bearing, then, in mind that the kidneys of Snakes are with rare exceptions wholly outside the peritoneal cavity4, and that the intestine commonly has no mesentery and bulges but little into the body-cavity, so as in individuals of some species (Liophis meremii) to appear to have almost entirely receded from it, it will be readily understood that this hinder peritoneal space may occasionally be reduced in Snakes to little more than a tube containing the 1 I add these remarks as to the kidneys because those organs are usually referred to in discussing the relations of the peritoneum, and the impression is sometimes conveyed that there is something unusual in the exclusion of the kidneys from the body-cavity. 2 The Amphisbsenidae [e. g. A. darwinii, Bepidosternon scutigerum, and to a rather less extent A. alba and Pachycalamus brevis] are the only marked exceptions I know of besides the Boa constrictor. 3 I could not ascertain the relations in Bamprophys, Hydrophis, and Crotalus, but have no reason to suspect them to be exceptional. 4 Tbe lymph-space mentioned above which may occur round them must not be mistaken for part of the peritoneal cavity. |