RETICULAR MATERIAL IN THYROID CELLS Da 
as Cajal (14, p. 215) records it in other gland cells, between the 
nucleus and the polo mundial, shows that the follicular cavities 
are to be considered from the phylogenetic point of view as being 
at one time in communication with the exterior (outside world). 
If further proof is needed that these spaces represent the lumen 
or duct of the ancestral gland, it is offered by the observation 
(Cowdry, ’21), that the cells bordering them are uniformly 
flagellated in the dogfish. 
We have, then, a remarkable coincidence. Apparently in the 
thyroid gland alone is there variability in the position of the 
reticular material, and in the thyroid gland alone have we clear 
evidence of physiologic reversal in the direction of secretion. In 
my opinion, the two phenomena are related. Since the position 
of the reticular material, like that of the centrosome, is a clue 
to the polarity of the cell, preparations made by Da Fano’s 
method will indicate the functional polarity, or, in other words, 
the direction in which secretion is taking place at the moment 
the preparations are made. This cannot be so safely inferred 
from a consideration of the height of the epithelium and the 
general appearance of the follicles as seen in routine hematoxylin 
and eosin preparations. Neither is the amount of colloid to be 
considered as a reliable clue, since it may have been produced 
during a storage phase which preceded the examination of the 
gland by a considerable interval of time. 
The relatively small percentage of reversals in the position of 
the reticular in the guinea-pigs which I have examined suggests 
that the balance in production of secretion is in favor of storage 
rather than of immediate discharge. Examination by Bensley’s 
method, which is probably more delicate since it is also more 
direct, would probably have failed to reveal any considerable 
amount of secretion antecedent near the perifollicular net. In 
the opossums, which he studied, in which the discharge into the 
perifollicular spaces is probably more marked, I would predict 
that the reticular material is often to be found between the 
nucleus and the discharging pole. Judging from his figures, it 
would appear that the nuclei have been forced toward the 
lumen by the accumulation of secretion antecedents near the 
periphery. 
