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Show MR. F. E. BEDDARD ON THE VASCULAR AND [May 1, and then the restriction of the membrane left; or, firstly the reduction in diameter of the lung and then the disappearance of the lung-tissue. That degeneration of this kind should occur in more than one way is not surprising. It may be obviously matched by parallel instances. It is well known that among the Boidse, for example, the lung, or lungs, extend, like those of Lizards, beyond (i. e. headwards of) the point of entrance of the bronchus into the lung. I have mentioned several instances in the present communication. This recess is enormously exaggerated in Ileterodon platyrhinos, as Prof. Cope (as well as others) has pointed out, and I can confirm him from the examination of several individuals. It is in this pocket of the lung that Prof. Cope seeks the origin of the tracheal lung, if I rightly interpret the following passage, viz. (loc. cit. p. 218):-" The dorsal lung may present proximally alongside of the trachea an auricle or pocket, and this is so developed in the genus Ileterodon as to reach to the head, without communication with the trachea, other than that furnished by the normal portion of the lung. In the Solenoglypha, without exception, this extension of the dorsal lung is present, and extends to the head, and its lumen is continuous with the trachea throughout its length. The same structure exists," &c. In the above-given account of various species of Ophidia, it will be seen that I have found the pocket in question to coexist with the rudiments of a tracheal lung independent of it. I cannot therefore accept Prof. Cope's view of the origin of the tracheal lung, and I put forward my own suggestions in its place. His attempt to classify Serpents by the character of the lungs will possibly form the groundwork of a more successful scheme. At present the facts are not sufficient for the elaboration of a complete arrangement of those Reptiles. Cope is probably justified in some of the details of the scheme, for example in the separation of the genus Ungalia from other Boas and Pythons. It is clear, however, that he is not necessarily right in separating Lepto-gnathinse from Scytalinse, for though the former doubtless possess a tracheal lung, I have shown that Erythrolamprus has considerable traces of one. In details I have myself pointed out that the characters of the lungs offer useful facts of assistance in classification. This is shown, for instance, among the species of the genus Coluber, and the minute points of likeness between Erythrolamprus and another Opisthoglyph genus, viz. Tarbophis, are noteworthy. The presence or absence of the rudimentary lung is obviously not so useful a character. The usefulness of the lung-structure in settling details of classification is also well shown in the case of Lioheterodon. This genus was confused by earlier systematists with the American Heterodon. Boulenger has shown *, utilising a structural peculiarity in the dorsal vertebrae first made use of by Prof. Cope, * B. M. Cat, Snakes, vol. i. 1893, p. 171. |