164 Proceedings of Royal Society of Edinburgh. [sess. 
demonstrated in embryos of this reptile the presence of right and 
left epiphysial outgrowths, which remain distinct and separate from 
each other. Of these, the left is the more important, and gives 
rise to the pineal eye, while the right never becomes transformed 
into anything resembling a pineal eye, but retains its attachment 
to the roof of the thalamencephalon, and constitutes the epiphysial 
stalk. So also in the chick the left evagination is the more important 
of the two. It is, however, unable to remain separate from the 
right evagination, and thus fails to retain its individuality.* 
Hill (17) has described right and left epiphysial evaginations in 
Teleosteans and in Amia ; but in the specimens examined by him 
the right outgrowth was somewhat more vigorous than the left, 
while they showed no tendency to blend with one another. 
Locy (19) has been another worker in this field of research. 
He describes the epiphysis of Elasmobranchs as developing from a 
pair of united accessory optic vesicles. In this group of Eishes, 
therefore, the paired elements tend to blend with one another as 
in the case of the chick and the Amphibia. 
This research was conducted in the Anatomy Department of the 
United College, University of St Andrews, under the terms of 
my appointment both as a Carnegie Fellow and as a Research 
Fellow of St Andrews University. I wish here to express my 
best thanks to Professor Musgrove for many valuable facilities 
which were afforded to me during the progress of the work. I 
intend to study the early stages of development of the epiphysis in 
Mammalia in order to ascertain whether any evidence of the bi- 
lateral condition of the epiphysis can be found in this class of 
Vertebrates. 
(3) Summary and Conclusions. 
(1) The epiphysis cerebri in the chick-embryo first appears in 
the form of right and left outgrowths or evaginations. Of these, 
the left is the better marked of the two. 
* My attention has been directed to a statement in Bateson’s Materials for 
the Study of Variation, to the effect that the functional eyes of Vertebrates, 
like other structures near the mesial plane, tend in certain rare instances to 
coalesce. This cyclopian condition has been described in the chick (see page 
458 of the above work), while on page 461 there is illustrated a specimen of 
the worker-bee ( Apis viellifica) with the two compound eyes fused together in 
the mesial plane. 
