50 Salisbury,— On the Structure and Relationships of 
numerous secretory sacs which permeate it throughout (PI. IV, Fig. 2 
In all respects the secretory elements of the interior appear to agree with 
those of the periphery. 
Each secretory sac is sheathed by a continuous layer of parenchymatous 
cells, which separate it off from the surrounding lacunar tissue. Component 
cells of this sheath are seen in tangential sections to have been vertically 
elongated and to have reached a length of some five times their width. 
Text-fig. 7. Plottings of the secretory sacs in three successive sections. In order to make the 
corresponding sacs more clear, they have been connected up by means of dotted lines. 
By carefully mapping the distribution of the secretory sacs between 
the same pair of ribs in successive sections of a series, one can recognize, 
from the relative positions which they occupy to one another, that the 
same sacs often extend for a considerable distance (Text-fig. 7). 
In the subjoined table an analysis of the results obtained from S. 31, 
b-i, is given ; the vertical series show the number of sacs in each section 
which can be traced back as far as that of which the designating letter 
