The pseudobranchial circulation in Amia calva. 13]. 



branch might as naturally acquire the position of the pseudobranch 

 as a mandibular one, and the relation of the pretrematic branch of 

 the glossopharyngeus to the organ would seem to indicate that it 

 is hyoidean rather than mandibular. It is thus largely by reason 

 of the comparison with Selachians that the pseudobranch of Amia 

 can be referred to the mandibular rather than to the hyoid arch. 

 In Lcpidosteus the pseudobranch seems to me to be developed in 

 much more definite and direct relation to the mandibular aortic 

 arch than it is in Amia, arising in Lejndosteus, according to Fried- 

 rich MÜLLER, in relation to capillary vessels that connect the two 

 arms of a loop secondarily formed in the mandibular artery. That 

 the opercular demibranch of Lepidosteus is hyoidean, and not man- 

 dibular, seems, from Müller's work, almost unquestionable, and 

 this conclusion certainly receives considerable support not only from 

 my work on Amia but also by comparison with the conditions found 

 in embryos of Selachians. 



Maurer, in his earlier work (5), says that in 11 mm embryos 

 of Esox lucius the pseudobranch receives two afferent currents, one 

 through the arteria hyoidea, which perforates the hyomandibular in 

 this fish instead of running across its anterior edge as in Amia, 

 and another from the carotid artery, through a branch that arises 

 from that artery at the point where it separates into what seem to 

 be its external and internal divisions. At this stage Esox thus seems 

 to almost exactly resemble embryos of Amia slightly older than 

 12 mm ones, and if the pseudobranch of the one is mandibular it 

 would seem that the other must be also. It is, however, not to be 

 overlooked that there seem to be both hyoidean and mandibular gills 

 in Lejndosteiis, and that either the one or the other, with its as- 

 sociated afferent artery, might be retained in Teleosts, or in certain 

 Teleosts. 



In his later work (6), which I have been able to consult through 

 the kindness of the Laboratoire Maritime Russe at Villefranche, 

 Maurer describes conditions in embryos of the trout that closely 

 agree with those in Amia, as far as they go. That section of the 

 postspiracular artery that lies, in Amia^ between the commissural 

 bar and the carotid artery, Maurer does not describe at any stage 

 in the trout; nor does he describe the ventral afferent artery that, in 

 Amia. runs backward into the gill cover. The arteria opercularis of 

 these later descriptions is said by Maurer to develop entirely from what 



