284. H. SAXTON BURR 
eral part in Amblystoma is an undifferentiated strio-amygdaloid 
body, characterized by the ventro-lateral olfactory tract, the 
lateral forebrain bundle and their connecting tracts. The dorso- 
medial part is the primordium hippocampi, receiving a small 
dorso-medial olfactory tract, but chiefly characterized by associa- 
tional fibers relating it with contiguous parts of the hemisphere 
and by strong tracts directly to the epithalamus and hypothala- 
mus. The dorso-lateral part is the relatively undifferentiated 
precursor of the lateral olfactory nucleus and pyriform lobe of 
higher brains, receiving (among others) the strong dorso-lateral 
olfactory tract, terminals of the lateral forebrain bundle, and 
associational fibers from the dorso-medial part. 
The analysis of the early phases in the development of these 
structures has been carried out on a series of larvae of Amblys- 
toma punctatum. Wax-plate models of the brains of five larval 
Amblystoma were made and checked by microscopic dissection 
of the entire brain. Drawings of three of these are shown in 
figures 13 to 18. In addition careful study was made of trans- 
verse sections stained in haematoxylin and erythrosin to deter- 
mine the microscopic relations. <A few of the critical sections are 
shown in figures 19 to 26. . 
It was noted in a previous paper that in general the form of the 
regenerating hemisphere followed the same pathway of develop- 
ment as the normal forebrain. Further analysis has shown that 
the detailed genesis pursues a similar course. This suggests a 
rather interesting problem. It has been shown that a regenera- 
ting hemisphere is derived from a thin layer of typical ependyma 
cells which bridge over the interventricular foramen after removal 
of the hemisphere (Burr, 716 b). These ependyma cells are 
derived from the ependymal cells surrounding the interventric- 
ular foramen. These are then new cells derived from cells not 
specifically involved in the cerebral evagination, and yet theses 
new cells are capable of developing a new hemisphere which 
repeats in its genesis the normal development of the forebrain. 
The question at once arises, is the pathway over which this de- 
velopment must go determined in the ependymal cells themselves 
or is it laid down by external factors dependent on the relation 
