1903-4.] Origin of the Epiphysis Cerebri in the Chick. 163 
while in the other cases this condition was distinctly evident after 
the 60th hour of incubation. 
Fig. 3 is, like the others, a transverse section of the thalam- 
encephalon in the pineal region, and is from a chick-embryo at 
the end of the 3rd day of incubation. This figure represents what 
might be termed the unpaired condition of the epiphysis. On 
close examination, however, the presence of two small angular 
recesses within the evagination will be noted, and it may be sug- 
gested that these are probably lingering evidences of the previously 
existing bilateral outgrowths — the process of coalescence having 
apparently just taken place. 
It therefore appears that what in its earlier stages of development 
used to be looked upon as a mesially placed epiphysial evagination 
is really situated to the left of the mesial plane , ivliile a more 
feebly formed evagination exists on the right side. This bilateral 
co7idition is, however , very transitory, and soon gives rise to the 
unpaired condition of the epiphysis by a coalescence of the 
primary elements. 
(2) Comparison of Results. 
The results of this research are of interest in so far as they 
support the observations previously made by the author in the 
Amphibia (8 and 9). They also agree in the main with the 
results obtained by various observers in reference to other classes 
of the Yertebrata. In Amphibia the author has described the 
presence in the early stages of right and left recesses from the roof 
of the thalamencephalon, of which the left is the better developed 
of the two j and has shown that these very soon coalesce to form a 
single epiphysial structure. It will be at once observed that these 
conclusions are corroborated in the case of the chick. 
It is also interesting to compare the results of the present re- 
search with those of Dendy (11) on Hatteria. This observer has 
