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Show 1895.] LUNGS OP SNAKES, AMPHISB.ENID.E, ETC. 707 VII. ON THE RATIONALE OP THE PACTS RECORDED IN THIS PAPER. Taking these Snakes and Snake-like forms together, the facts noted in this paper are that while some agree with other air-breathing vertebrates in having two lungs well developed, some have one lung quite rudimentary or absent altogether, and that of these latter some have the right lung rudimentary or absent and some the left. These facts suggest the questions - M a y we reasonably conclude that in the ancestors of all the different groups of pulmonate vertebrates the lungs were essentially similar in their first origin ? If so, what was probably the most primitive condition ? What significance may we attach to a divergence from such common condition of the kind above described ? 1 I have also examined two specimens of Lygosoma verreauxii. In the first I was at first surprised to find the right lung apparently shorter than the left (contrary to the rule), but on further inspection I found that this condition was purely pathological, being due to the presence of a small tumour on the anterior border of the right lobe of the liver which interfered with the expansion of the lung. In a second specimen the lungs were of precisely equal length. This equality of the lungs in L. verreauxii and occasionally in Anguis fragilis (see list) makes m e expect that (while the elongated snake-like form and the reduction or suppression of the limbs are commonly associated with the reduction of one lung) the lungs may be found equal in a number of the other elongated small-limbed lizards of which there are so many, especially in the family Scincidce. 2 J. von Bedriaga (Archiv fur Naturgeschichte, 1884, Bd. i. p. 63) finds no trace of a second lung in Blanus (Amph.J cinereus and B. strauchii and Trogonophis wiegmanni; and C. Smalian (Zeitschrift fur wissensch. Zool., Bd. xiii. pp. 188 & 189,1885) finds no trace of a second in A. fuliginosa, B. cinereus, and Anops kingii, while as to Trogonophis wiegmanni he curiously prefers to regard it as having a bilobed single lung instead of a pair of lungs. Neither Bedriaga nor Smalian, so far as I have discovered, say which lung is well developed, but Bedriaga's figures of B. cinerea (I. c. pi. iv. figs. 2, 3) rightly represent it as the left. 3 I have examined other Amphibia, especially the elongated forms with weak limbs and reduction of digits or absence of one pair of limbs (Siren); but in none of them can one lung be said to be atrophied as compared with the other. In most of them the two lungs are of equal length [Siren lacertina, Menobranchus lateralis, Menopoma alleghanense, Salamandra maculosa, Triton cristatus, Amblystoma tigrinum (fair-sized specimens of Axolotl)]. In a few cases there is a difference in the length. Thus in Amphiuma the right lung is the longer, while in Proteus anguinus, as is known from the published figures, the left is somewhat tbe longer, and the same appeared to be the case in some small specimens of Axolotl. These last two can hardly, however, be regarded as exceptions to the general rule, for we cannot say that the right lung is atrophied as compared with the left. Thus each lung of Proteus extends back to the ovary or testis, and the fact that the right lung is the shorter depends on the fact that in accordance with a common habit the right reproductive gland is situated further forward than the left. Again, though recording it for form's sake, I hardly think any stress should be laid on the right lung appearing shorter than the left in small (3 inches long) specimens of Axolotl. The lungs are equal in later stages, and the apparent difference in the younger specimens is probably due to tbe small intestine, which inclines to the right side, presenting the complete expansion of the terminal portion of the right lung, which projects backwards freely beyond the termination of the lung ligament. |