SYSTEM or SACCOBEANCHUS FOSSILIS. 53 



Having regard to the fact that Eamsay Wriglit's figure is a 

 diagram in the Introduction to a Greneral ISTatural History of 

 Fishes ' *, but that Boas, on the other hand, was working specially 

 upon the aortic arches of these Ganoids, it seems to me that we 

 are justified in electing to follow Boas ia this matter, and, with 

 him, to look upon the pulmonary artery of Polypterus and Amia 

 as a derivative of the fourth aortic arch alone f- 



Finally, we come to the mixed group of tropical freshwater fishes 

 in which a modification of the pharyngeal region does duty as a 

 lung. The anatomy of the epibranchial organ of the Labyrinthici 

 has been worked out by Zograff % '■> ^^*i ^s regards the blood- 

 supply to that structure, he succeeded, after several disappoint- 

 ments, in proving that the blood is brought to the epibranchial 

 organ by the fourth aortic arch. 



The suprabranchial chamber of the Ophiocephalidae, which so 

 much resembles that of the Labyrinthici, according to Hyrtl 

 does not receive its blood from the heart, although the fourth 

 branchial artery passes through it. From the subsequent experi- 

 ments that have been performed on these fishes, it is very 

 probable that Hyrtl was mistaken, and that these chambers are 

 organs for the respiration of air. In this connection it is 

 well to remember that Zogralf found great difficulty in injecting 

 the blood-vessels to the epibranchial organ in the Labyrinthici. 



Now, as to Saccohranchus, we have seen that Hyrtl and 

 Hubrecht found that the blood was carried to the respiratory 

 sacs by the first aortic arch on one side, and the fourth on the 

 other. In my specimen, on the contrary, it was supplied by the 

 fourth on both sides. 



The peculiar spirally-coiled epibranchial organ of Heterotis 

 Ehrenherqii, one of the Osteoglossidae §, receives its blood from 

 the fourth aortic arch, as also does that of Chanos salmonceiis 

 {Lutodeira cJianos of Hyrtl) ||. In the Cuchia eel, Amphipnous 



* Ramsay Wright, ' Standard Natural Histoi-j-,' vol. iii. p. 48. 



t Boas, Morph. Jabrb. Bd. vi. pp. 342 & 351. 



+ ZografF, Quart. Journ. Micros. Sci. vol. xxviii. 1888, p. 501, "On the Con- 

 struction and Purpose of the so-called Labyrinthine Apparatus of the Laby- 

 rinthic Fishes." 



§ Hyrtl, Dentschr. Akad. Wiss. Bd. viii. 1854, p. 73, "Beitrag zur Anatomie 

 Ton Heterotis Ehrenbergii." 



II Hyrtl, " Ueber das Epigonale Kiemenorgan von Lutodeira chanos," 

 Deuksdir. Akad. Wiss. Bd. xxi. 1803, p. 1. 



