560 D, L. GAMBLE 



In the transitional region between the trunk and tail no sepa- 

 rate haemapophyses were found in any of the larvae studied. 

 The haemal arch is formed by the downgrowth of the bases of the 

 parapophysis and not by the elongation of distinct haemapophyses, 

 as in Salamandra and Amblystoma. 



In the 25-mm. larva (fig. 25) in the last trunk vertebra the 

 proximal portion of the basal stump shows a tendency to bulge 

 downward. On one side this is very noticeable, while on the 

 other the process is in an incipient stage. On the left the proxi- 

 mal portion of the basal stump bends downward considerably 

 below the horizontal septum. A short distance from the noto- 

 chord, growth apparently is taking place in two directions, 

 laterally to form the lateral process and ventrally to form the 

 haemal-arch element. The more ventral outgrowth becomes 

 dominant over the lateral one and leaves it behind, so that it 

 appears as a lateral process of the haemapophysis. On the other 

 side the ventral outgrowth has not yet become dominant over the 

 lateral and appears here only as a rounded knob projecting sHghtly 

 ventrad from the base of the parapophysis (fig. 25). 



In the first tail vertebra of the same larva (fig. 26) both haema- 

 pophyses have developed ventrally and completed the haemal 

 arch below. The parapophysis appears as a small lateral process 

 of the haemal arch. In the second tail vertebra this lateral 

 process has lost its connection with the haemal arch and exists 

 as an independent element (fig. 27, h.a.). 



It is seen, therefore, that the basal stump of Necturus shows a 

 tendency to fork not only in this region, but also farther forward 

 in the trunk of younger larvae. Anteriorly the lateral division 

 becomes dominant as the parapophysis and the lateral disappears, 

 while posteriorly the ventral one becomes dominant as the haema- 

 pophysis and the ventral disappears. 



These two divisions of the basal stump, however, tend to sepa- 

 rate secondarily not only in the anterior tail region, but also in 

 the trunk. This separation is permanent in other salamanders 

 and in Polypterus, but, as Goeppert states, such cases in all 

 probabiUty represent a secondary separation. 



