REACTIONS OF MELANOPHORES OF AMBLYSTOMA 



243 



figures 4 and 5 (of larvae 14.5 and 34.0 mm. long respectively), 

 the later development of these parts of the roof of the brain are 

 shown. The condition seen in figure 5 is typical of older larvae 

 and of adult Amblystoma, although it must be said that the open- 



'Sifer 



^ 





■^ 









V. ^ 

 RA 





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1 2 



Fig. 1 The anterior end of asagittalsectionof a5.3mm.larvaof A. punctatum. 



Ep.A., epiphysal arch; P. A., paraphysal arch; P.V.A., post-velar arch; V., 



velum. 



Fig. 2 The anterior end of a sagittal section of a 6.6 mm. larva. 



ing into the stalk of the epiphysis cannot always be made out 

 with great distinctness, so that there is a question as to whether 

 it may not later be solid instead of hollow as here represented. 

 In no case, however, w^as the epiphysis found not attached to the 

 brain. Its cavity is more or less incompletely divided by septa. 



