OCR Text |
Show 1906.] RESPIRATORY SYSTEMS IN THE OPHIDIA. 521 up, when adopting a threatening demeanour, to an unusual extent. It will be observed that the tracheal lung of Coluber corais is planned on the model of that of the Viperidse. But instead of being vascular as in those Snakes, it is just the part of the lung which is non-vascular, the vascularity commencing with the thoracic lung. In the Vipers it is the tracheal lung which is vascular and the thoracic lung which is not so. I am fortunately able to compare the state of affairs in this species Coluber corais with that of other species of the genus Coluber. These will now be dealt with. In Coluber longissimus (-C. cesculapii) there is also a tracheal lung, which is, however, different in detail from that of C. corais. The lung-tissue is, as usual, continuous with the dorsal membranous interval between the tips of the incomplete tracheal rings. This interval is narrow as in Serpents, with no tracheal lung; but for some distance, an inch or so, in front of the heart it has the honeycombed structure of the lung proper. This fades away gradually anteriorly into the ordinary membranous appearance of this part of the respiratory apparatus in those Ophidia which possess no tracheal lung. It does not seem to be vascular except perhaps just at its commencement below, and has not the pink colour characteristic of the functional lung. There is a rudimentary second lung which is vascular as in Coluber corais, and the existence of which has.been duly noted by G. W. Butler*. Coluber obsoletus (= alleghaniensis). - In a spirit-preserved example of this Coluber there are also traces of the tracheal lung invading the membrane for some little distance in front of the heart. There is also in this species a very distinct headwardly directed caecum of the lung, as in other species of Coluber. There is also present the second though rudimentary lung, which is, however, cellular in structure and not a mere thin-walled sac. The orifice into the second lung is exactly on a level with the apex of the heart. The orifice has the form of a perforation of the tracheal gutter. It does not lie in the lung-substance beside it. The tracheal gutter is in this species fairly extensive. It can be traced easily to a point lying about half an inch behind the commencement of the liver, that is about 4 inches behind the apex of the heart. Its termination coincides with the end of the vascular region of the lung. The total length of the Snake itself from mouth to vent is 47 inches. Coluber leopardinus, though a small Snake like Coluber longissimus, has vestiges of the tracheal lung more like those of the large Coluber corais. It resembles that species, in fact, by reason of the great width of the anangious membrane which divides the tracheal rings at their tips anteriorly. The honeycomb structure of the lun«' extends for a shorter distance than in Coluber longissimus in front of the heart, and in this region the width of the " lung " is less than anteriorly. Close to the apex of the heart-a little in * P. Z. S. 1895, y. 705. |