324 Miscellaneous. 



series of circular orifices, of which the upper are the efferent orifices 

 of the pulmonary arch, and the lower are the afferent orifices of the 

 floor of the lung. On this floor, in fact, the vessels which originate 

 from these orifices ramify in a network of which the efferent 

 branches converge into a large trunk, entirely overlooked by M. 

 Jourdain, and which, collecting the blood of the whole of the floor 

 of the lung, empties itself directly into the auricle. From this 

 results the fact, entirely exceptional in the Pectinibranchiata, that 

 the auricle receives two totally distinct afferent veins. The one is 

 branchial and pulmonary, the other exclusively pulmonary. This 

 is a remarkable peculiarity of the anatomy of the Ampullarice, 

 which is in connexion with the double respiration of these animals, 

 and with the alternations in function of the double respiratory ap- 

 paratus. 



The afferent vessel of the branchia and the proper afferent vessel 

 of the lung meet in front in such a manner as to form an anterior 

 arch. The intermediate trunk meets this arcade very obliquely and 

 under a very sharp angle open to the left. There is thus formed 

 between the two vessels a valvular spur, which plays an important 

 part in several respects. When, during sojourn in the water, the 

 pulmonary respiration and circulation are suspended by the want 

 of air and the collapse of the lung, the blood of the proper afferent 

 vessel of the lung, being unable to traverse the pulmonary network, 

 arrives in abundance at the level of the mouth of the intermediary 

 trunk, to which it applies the valvule and which it thus stops. It 

 is thus obliged to pass entirely into the afferent vessel of the 

 branchia, and, consequently, into the branchia, of which the activity 

 is thus greatly increased. When, on the contrary, during sojourn 

 in the air, the collapsed branchia does not act, the blood of the 

 afferent vessel of the branchia, arriving en masse on the edge of the 

 spur, there divides into two currents, one of which penetrates into 

 the proper afferent vessel of the lung, and the other into the inter- 

 mediary trunk, of which it augments the tension, and which distri- 

 butes a part of it to the floor of the lung, and reconducts the rest to 

 the heart. By this means the activity of the pulmonary circulation 

 is increased during the repose of the branchia. Hence results this 

 interesting fact, that the Ampullarice, which are Pectinibranchiata 

 in which pulmonary respiration has made its appearance, have the 

 respiratory vessels disposed in such a manner that, when this newly- 

 introduced function suspends its activity, all the blood which should 

 have traversed the pulmonary network is constrained to traverse 

 the branchial system, where its hsematosis is assured. This curious 

 arrangement may suffice to explain the preservation of the branchia 

 in Gasteropoda, in which the lung has attained so remarkable a 

 development, and which might have become purely pulmonary 

 animals. 



The distribution of the vessels in the pulmonary walls merits 

 special mention. They form a double system of portal veins ; that 



