640 FRANCIS M. BALDWIN 



Maurer used the term (in Triton, Siredon, and Salamandra) , and 

 not ' suprapericardial ' (van Bemmeln) as Miss Piatt found it in 

 Necturus. The body is caudal to the last gill-pouch (fifth vis- 

 ceral or fourth branchial) in about the position where one would 

 expect to find a sixth visceral pouch (fifth branchial), and not 

 cephalad to the posterior pouch as in Necturus. As a rule, the 

 body in Amblystoma is asymmetrical in its development, usually 

 occurring on the left side (in this respect agrees with Triton and 

 Salamandra) but in one individual (19 mm. larva, see below) it 

 appears on the right side as well, and 'in this stage more closely 

 agrees with the conditions described for Necturus (Miss Piatt 

 '96) and Hypogeophis (Marcus '08), although the body on the 

 right is smaller, and possibly persists but a short time. 



A. Amblystoma larvae, S mm. long. The earliest stage in 

 which the anlage of the body is recognized with certainty in my 

 material is in larvae 8 mm. long. Maurer distinguished it earlier 

 in Triton, even in an embryo before hatching, but Miss Piatt, 

 begins her description of it in Necturus, with a much larger 

 stage, (15 mm.). Since the region of the body where the anlage 

 occurs has been described in some detail in the discussion of the 

 thymus, it is only necessary to say here that the first appearance 

 of the postbranchial body is in sections which pass through the 

 ganglion of the vagus. Here, on the left side, a portion of the 

 ventral floor of the pharynx, between the anlage of the fourth 

 branchial pouch (fifth visceral), and the anlage of the glottis, 

 becomes slightly thickened. The exact extent of this thickening 

 — both laterally and anterio-posteriorly — at this stage is impos- 

 sible to define, as it fades out on all sides, but cells in its central 

 region begin to extend ventrally into the connective tissue above 

 the pericardial wall there to form the anlage of the postbranchial 

 body. Figure 10a is through the thickened portion where the 

 ventral cells forming the postbranchial anlage is most pronounced. 

 The lateral limits of this anlage are marked roughly at points r-r, 

 medial to which is the anlage of the glottis, and lateral to which is 

 the anlage of the fourth branchial pouch, while four or five large 

 procartilage cells below them mark the position of the anlage of 

 the fourth branchial arch. At this time there is no other notice- 



