SYSTEM OF SACCOBRANCHTJS FOSSILIS. 55 



I cannot conclude without tendering my warmest thanks to 

 Prof. Howes for the trouble he has taken in helping me with this 

 paper, and for many kindly suggestions and corrections. 



Note (25 Sept., 1894). — Since writing the above, my attention 

 has been called to two short papers by Jobert on the aerial 

 respiration of certain fishes of the Amazon (Ann. Sci. Nat. ser. 6, 

 vol. V. art. 8, & vol. vii. art. 5). In three instances {Oalliclithys, 

 Mypostomos, and Doras) aerial respiration is effected by means of 

 a peculiarly modified portion of the intestine which receives its 

 blood-supply from the aorta ; the blood, however, is partly venous, 

 as the afferent and eff'erent branchial vessels are continuous and 

 allow the blood to pass directly from one to the other. In the 

 case of two other fishes {Erythrinus and Sudis) the swim-bladder 

 functions as a lung, receiving venous blood from the mesenteric 

 veins, and also arterial blood from the aorta. It will be noticed 

 that all these fishes, as regards their pulmonary blood-supply, 

 are exceptions to the general tendency indicated above : that this 

 should be so, especially in the case of the intestinal breathers, is 

 not a matter for surprise ; here, if anywhere, one would expect 

 to find variation, for the distance of the modified organ from the 

 pharynx suggests the probability that the blood-supply to the 

 newly acquired lung might be procured from some already exist- 

 ing neighbouring vessel, rather than directly from the distant 

 aortic arch. — R. H. B. 



lilNN. JOTJEN. — ZOOLOGT, VOL. XXT 



