8&4 Transactions of the Academy of Science of St. Louis 
midial granules aggregated in the peripheral zone, and chromidial 
dust occupying the remainder of the cytoplasm of the cell body. 
Central somatic efferent neurons are cytologically similar to 
peripheral somatic efferent neurons. Their chromidia are coarse 
and occur as discreet units which are fairly uniformly distributed 
throughout the cell body. Most of them are polyhedral but 
some are nearly spherical in form. The central visceral efferent 
neurons are, in general, medium-sized, spherical or polyhedral 
cells with chromidia which are somewhat more granular than 
those of the associational neurons. The chromidia ferquently 
are aggregated in the peripheral zone but sometimes occur 
clumped in certain portions of the cytoplasm. Associational 
neurons are characterized by relatively very small size, fusiform 
or spherical shape, and a perinuclear distribution of the chro- 
midia. 
The majority of the neurons in the hypothalamus of the cat 
are central visceral efferent; next in abundance are the associa- 
tional neurons. In those nuclei which contain central somatic 
efferent neurons and in those in which the more specialized 
visceral efferent neurons occur, associational and central visceral 
efferent neurons also are present in considerable abundance. 
In view of the diverse sources of the afferent fibers and the 
connections effected by the efferent fibers which recently have 
been described for the various hypothalamic nuclei, most of 
these nuclei must include central visceral efferent and associa- 
tional neurons and some of them also central somatic efferent 
neurons. In view of the finding that certain neurons in the 
nucleus supraopticus give rise to fibers which end in functional 
relationship to secretory cells of the posterior lobe of the hy- 
pophysis, the distinctive cytological characters of these cells also 
can be correlated with those of other peripheral visceral efferent 
neurons. 
