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first close together but, as growth proceeds they are carried further 
apart. The first formed attachment retains its median position, but 
the second complex one (a and 0) becomes lateral through unequal 
growth of the brain walls. The same process leads also to the elon- 
gation of the median nerve (nv) and to a change in the relative posi- 
tion of the olfactory cup. The long axis of the latter is at first 
verticle in reference to the head but gradually comes to lie trans- 
versely to it. 
Fig. 2 represents a view on the front surface of the right half 
of the brain of an older embryo (33 mm in length). Part of the 
Fig. 2. > about 30 diameters. 
olfactory cup has been broken away exposing the nasal membrane 
which is already thrown into folds. It shows better than the preceeding 
Fig. that there are two distinct elements combined in the olfactory 
nerve — a median dorsal (mv) and a lateral one (a and b). The median 
nerve is relatively long and slender and still shows an enlargement 
near its central connection. It passes obliquely across the surface of 
the fore-brain and unites with the lateral bundles which are larger 
and more complex than in the earlier stage. 
The lateral element, which comes to be the main olfactory, con- 
sists of two main divisions (a) and (0). These are in turn subdivided 
so we have two separated clusters of smaller bundles. The division 
(a) has one large fnd two slender nerves that branch in an arborescent 
