460 Leland Griggs. 



to correspond to the segments of the neural plate (fig. 4, B), 

 Dut the crest on the upper surface and on the outer edge is smooth 

 except in a very few cases where some of the grooves between 

 the neuromeres are extended laterally clear across the crest. 

 This description differs from that of Locy ('95) who has pictured 

 for Amblystoma not only a few large neuromeres in the open 

 neural plate but also a beaded appearance in the neural crests. 

 This beaded appearance was not apparent in any of the embryos 

 of this stage used in the preparation of this paper. 



The neural crests in this stage begin to move in toward the 

 median line. The change is seen first at the posterior end of 

 the neural plate where the two crests meet just in front of the 

 anus (fig. 5, E). The anus which is now dorsal in position sooq 

 noves to a ventral position and loses all connection with the 

 neural crests. In this respect Amblystoma seems to agree 

 exactly with the condition which Morgan ('97) has described in 

 detail for Rana. One point in addition should be noted. The 

 infoldings which in the earlier stages extended for a short distance 

 to the right and the left of the anus now fade away and disappear 

 as can be seen by a comparison of A and E in fig. 5. Further 

 changes in connection with the moving in of the neural crests 

 will be described as they are pictured in connection with older 

 stages. 



The neural groove, the origin of which has already been traced, 

 is easily recognized in all embryos (fig. 4, A, B). The posterior 

 germinal depression with which the neural groove might be con- 

 fused has now disappeared except in a very few eggs and the 

 only remaining part of the anterior depression is the deep pit 

 which has been shown in the preceding stage. The blastogroove 

 disappears from view as the neural crests close over and in a 

 majority of eggs it can no longer be distinguished from the neural 

 groove (fig. 5, E). This condition of the various grooves per- 

 sists until the neural canal is completely closed. 



The open neural plate with its various structures, grooves, 

 crests, neuromeres, etc., has now reached its maximum develop- 

 ment. Fig. 5, F, is a diagram illustrating the different struc- 

 tures, all of which appear in every egg in the course of its develop- 



