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Show 1895.] LUNGS OP SNAKES, AMPHISB^ENID^E, ETC. 711 nearly all air-breathers, but that this only leads to inequality some secondary cause, such as the acquisition of a slender snakelike habit of body (or in mammals some other cause, see § VII.), is superadded. Moreover, it would appear that in some cases (as in most Snakes), the inequality once started, the replacement of paired lungs by one larger one has in its turn led to a further displacement of the alimentary canal and other organs. While thus suggesting an order of priority for correlated modifications, the writer does not lose sight of the fact that these modifications have all arisen under the supervision of Natural Selection, and that the safest and most philosophical course is simply to say that the aggregate of modifications are in some way more or less advantageous. 6. The question occurred to me whether the complete or partial suppression of the right lung peculiar to Amphisbaenidae might serve to tell us anything as to the stage in their evolution at which the Amphisbaenidae branched off from the stock common to them and other Lizards-whether, for instance, it might indicate that they branched off before their common ancestors had acquired lungs, at a time, therefore, when perhaps the respective ancestors of existing Lacertilia and Amphibia had diverged comparatively little However, on consideration it seems clear that the facts here recorded do not by themselves prove any such thing, and that they are not by themselves inconsistent with a considerably later separation of the Amphisbaenians. 7. This peculiarity of the Amphisbaenian lungs is for the present, then, but one added to the list of the peculiarities of these very interesting animals ; but the fact that (so far I have been able to ascertaiu) no other vertebrate has the right lung suppressed, suggests that tbis at first sight unimportant character may be found to be correlated with some other character the significance and importance of which may be more obvious. IX. BIBLIOGRAPHY \ (1) C H R . LUD. NITZSCH. De Eespiratione Animalium, p. 13. Vitebergas, 1808. (2) J. P. MECKEL. " Ueber die Eespiration der Reptilien." Deutsches Archiv fur die Physiologie, Bd. iv. pp. 60-89 [especially p. 84] and plate 2 [of which the explanation is given at the end of Heft 1, pp. 162-164]. Halle, 1818. (3) J. P. M E C K E L . System der vergleichenden Anatomie, Bd. vi. pp. 257-262 [especially pp. 257 and 260]. Halle, 1833. (4) Lecons dAnatomie comparee de Georges Cuvier, redigees et publiees par G. L. Duvernoy. 2nd ed., torn. vii. pp. 19- 163. Paris, 1840. 1 Milne-Edwards (6) refers to a separate paper by Lereboullet entitled 1 Anatomie compared de l'appareil respiratoire.' None of the London Libraries accessible to m e possess a copy of this paper; so I have not been able to see it, and consequently do not put it on the list, but it is possibly quite as worthy of a place there as some of the others. |
