498 WILLIAM H. F. ADDISON 
with some uncertainty, due to lack of definite information, the 
toothed whales in general. 
As is well known, the Cetacea, as a result of their conformation 
to an aquatic mode of life, have undergone many changes in their 
structural peculiarities, but in no system perhaps are these 
changes more striking than in the organs concerned with olfac- 
tion. In the adult animals, the turbinates are relatively much 
reduced in size, the cribriform plate of the ethmoid is imper- 
forate or may have only a single pair of openings, while the 
olfactory bulbs and tracts are represented by slight remnants 
or disappear entirely. The whole apparatus for the sense of 
smell is much reduced, thus rendering very appropriate the terms 
microsmatic and anosmatic to the different members of this . 
order. Whether the anosmatics, like other mammals, have 
olfactory tracts and bulbs during fetal life, has not been care- 
fully studied but it is certain that they lack them entirely in the 
mature animals. Thus, as stated above, there is not the slight- 
est trace of these structures in the adult dolphin’s brain. 
Because of the disappearance of these external portions of the 
rhinencephalon, it has been interesting to study the more cen- 
trally placed parts of the olfactory mechanism, in order to see the 
extent of their regression. The brain of the dolphin has been 
studied from the same point of view by Broca (’79) and Zucker- 
kandl (87). Their observations, however, were restricted for 
the most part to the external form and gross relations. 
MATERIAL STUDIED 
At the Frankfurt Neurological Institute, conducted under the 
direction of Professor Edinger, to whom I am greatly indebted, 
during the summer of 1914, I had the opportunity of examining 
thin sections of the brain of an adult dolphin. The sections were 
cut serially, and every third section stained by Weigert’s myelin 
method. Each section was mounted on a separate plate of glass 
and covered with gelatine by the method worked out in the 
Frankfurt laboratory. In addition, five hemispheres, preserved 
in formalin, were available for gross study. These brains were 
