OLFACTORY CENTERS IN TELEOSTS emi. 
part of the same set of association fibers. The connections include 
all the nucleus preopticus-nucleus intermedius, posthabenularis, 
ganglia habenularum, nucleus commissuralis, nucleus entopedun- 
cularis connections (fig. 140). Such connections also exist between 
the corpus precommissurale and the primordium hippocampi. 
Commissural connections 
These include the commissura interbulbaris between the two 
olfactory bulbs (?); the commissura hippocampi, pars anterior 
connecting the two primordia hippocampi or nuclei dorsales; 
the commissura hippocampi, pars posterior, Joining the lobi pyri- 
formes; the commissura corporium precommissuralium, between 
the partes supracommissurales; and the commissurae nucleorum 
preopticorum, all present in the anterior commissure. The pyri- 
form lobes may also be connected through the superior or haben- 
ular commissure forming a commissura aberrans. 
The formatio reticularis 
In any discussion of the different pathways it must never be 
forgotten that the fine, reticular network of the formatio reticu- 
laris type is of great functional importance. In the past the 
tendency has been to consider only the tracts laid down in definite 
bundles. It is probable that in the phylogeny of a fiber tract the 
heavily myelinated bundle is the latest stage. In early stages, 
different areas are connected by a diffuse network of unmedul- 
lated fibers, through which impulses may take many courses. As 
phylogenetic development proceeds, impulses tend to take more 
and more definite paths through the maze of the reticulum; 
thus the diffuse unmedullated fiber connection is formed. Next 
this diffuse connection becomes more compact and usually myelin- 
ated. It should not be implied that the myelinated tract is more 
efficient for all connections, as it probably comes into existence 
chiefly when there is necessity for a stereotyped reflex; to prevent, 
possibly, ‘loss of current’ through diffusion, to use an electrical 
analogy. In spite of this, there is no question but that the more 
diffuse connections are of the utmost importance in putting into 
