574 Proceedings of Royal Society of Edinburgh. [sess. 
some of the pigment may lie free in the epiphysial recesses, and 
thus render their presence somewhat indistinct (see fig. 3). 
The period of existence of this primary bilobed condition of the 
epiphysis is a very transient one, for by the twelfth day of develop- 
ment in the frog the right recess has quite disappeared, while the 
left one still persists. The latter has progressed in development 
so as to form a well marked evagination from the roof of the 
fore-brain, and the effect of this active growth is to cause its open- 
ing to become situated to the left of the mesial plane. According 
to this description, then, the right recess would seem to disappear 
entirely. Fig. 2 shows the condition of the epiphysial evagina- 
tion in a twelfth day frog-embryo (6 mm. long). It will he 
observed to he placed distinctly to the left of the mesial plane, 
while the roof of the fore-brain has become somewhat diminished 
in thickness. 
The question at once arises, What is the fate of the right 
epiphysial recess ? The answer to this appears to he furnished by 
an examination of the series of toad-tadpoles. These were all 
stained by a special mode of application of the iron-alum- 
haematoxylin (Heidenhain) stain. 1 By this method the nuclei in 
the walls of the right and left epiphysial recesses were found to be 
stained of a deeper tint than the other nuclei in the wall of the 
cerebral vesicles. This appearance has been represented in fig. 3, 
in which the area of deeply staining nuclei will he observed to he 
well mapped off from those which are immediately adjoining — the 
latter being stained of a lighter tint. This figure is taken from a 
toad-embryo (4*5 mm. long ; ten days after fertilisation), and shows 
a somewhat late stage of the bilateral condition ; for the left recess 
is beginning to take on increased growth, while the right recess is 
seen to he feebly developed, and obscured by pigment. 
Fig. 4 is taken from a somewhat older toad-tadpole. The 
epiphysial evagination is here represented as being placed to the 
left of the mesial plane, and its walls are seen to be composed of 
the deeply staining nuclei — the latter being entirely confined to 
this region. This appearance affords strong proof of the fact that 
the right recess terminates its existence by blending with the left 
1 The application of this mode of staining will be described in extenso in 
another paper. 
