The pseudoNranchial circulation in Amia calva. lOI 



with the efferent pseudobranchial artery. The efferent artery extends 

 backward a certain distance beyond the point where it is joined by 

 the primary afferent one, so that the hitter artery appears as a 

 branch of the former, and doubtless acts as such, transmitting blood 

 from the carotid, and hence being traversed by a current running in 

 the opposite direction to the one found in 12 mm larvae. The i)ri- 

 mary afferent artery has, in its dorsal portion, the same course that 

 it has in young larvae, but it was not traced downward for any con- 

 siderable distance. The pseudobranch, at this age, has, in serial 

 transverse sections, an oval or kidney- shaped form, the long axis of 

 these sections of the organ inclining upward and mesially toward the 

 pseudobranchial cleft, at an angle approaching a right angle. The 

 dorso-mesial end of the pseudobranch is smaller than its ventro-lateral 

 end, and abuts against the epithelial lining of the chamber of the 

 cleft, excepting in its anterior portion, where the organ extends for- 

 ward beyond the chamber. Elsewhere the organ is separated from 

 the cleft and from the mouth cavity by a considerable space. The 

 secondary afferent pseudobranchial artery lies longitudinally along the 

 rounded dorsal surface of the pseudobranch, slightly lateral to that 

 part of the organ that abuts against its cleft. The efferent artery 

 lies along the ventro-mesial surface of the pseudobranch, up about 

 one quarter of the length of the transverse section of the organ from 

 its ventral end. The pseudobranch itself extended, in this specimen, 

 through 127 sections each 10 [.i in thickness. 29 of these sections 

 lay anterior to the oral opening of the cleft. That part of the latter 

 opening that lies ventral to the pseudobranch extended through the 

 next 25 sections. The diverticular extension of the cleft began 2S 

 sections posterior to the anterior end of the pseudobranchial chamber 

 and extended backward to the level of the oral opening of the cleft, 

 that is through 45 sections. Little spicules of dermal bone lined both 

 edges of the oral opening of the cleft, being most developed in the 

 lateral edge. 



The ventral portion of the primary afferent pseudobranchial artery 

 arises in 50 mm specimens, as it does in 12 mm ones, from the ventral end 

 of the efferent artery of the first branchial arch, and it there has two 

 roots, as Friedrich Müller says it also has in 16 mm embryos of Lepi- 

 dosteus. Whether it is directly continuous with the ventral end or ends 

 of the efferent artery, or is separated from that artery by a cai)il]ary 

 space, as Müller shows in his figures of Lepidosteus^ w\t,s not investi- 

 gated. At first a fairly large vessel it runs downward and forward lateral 



