130 EDWARD PHELPS ALLIS jr., 



efferent hyoiclean artery it receives what Dohrn describes as a 

 "Zustrom aus Blutmassen des Spritzlochbogens". Beyond this point 

 the carotid artery, after connecting with its fellow of the opposite 

 side of the head immediately behind the hypophysis, is joined by 

 the efferent artery of the spiracular gill, this latter artery being 

 called by Dohrn the carotis interna anterior. 



The afferent and efferent hyoidean arteries of Selachian embryos, 

 taken together, thus closely resemble the single postspiracular vessel 

 of Amia; and the prespiracular or mandibular vessels, in the two 

 fishes, would bear an equally striking resemblance if the efferent 

 and secondary afferent pseudobranchial arteries of Amia, plus a 

 certain portion of the external carotid, were the homologues, re- 

 spectively, of the carotis interna anterior of Selachians and the vessel 

 that Dohrn refers to as one that transmits the "Zustrom aus Blut- 

 massen des Spritzlochbogens". That these two pseudobranchial ar- 

 teries of Amia are the homologues of the two arteries of Selachians 

 can certainly not be positively affirmed, but it seems to me that 

 there is much in favour of the assumption. That the ventral por- 

 tions of the afferent mandibular and hyoidean arteries of Selachians 

 are the homologues of the corresponding portions of the same vessels 

 in Amia seems to me unquestionable, as a comparison of my Figures 

 4 and 10 will show. It thus seems necessarily to follow that the 

 pseudobranch of Amia is the homologue of the spiracular demi- 

 branch, or pseudobranch, of Selachians. 



The pseudobranch, in Amia, although it develops in relation to 

 a section of the mandibular aortic arch, does not receive its entire 

 blood supply through that aortic arch, a part of it coming through 

 the hyoidean aortic arch. At about the epoch when the pseudo- 

 branch can be considered as becoming, embryologically, a definite 

 organ, that is in 12 mm larvae, its blood supply is derived either 

 entirely from the efferent artery of the first branchial arch, or partly 

 from that artery and partly from the hyoidean artery, none of it 

 coming through what could be considered as a mandibular aortic 

 connection with the ventral arterial trunk. Later the blood supply 

 is probably derived entirely from the external carotid. There thus 

 seems no definite reason to ascribe the organ, in so far as its blood 

 supply alone is concerned, to the mandibular rather than to the 

 hyoidean arch. Moreover, in the gradual closing of the ventral 

 portion of the spiracular cleft it would seem as if a hyoidean demi- 



