564 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
become arranged to form a narrow cylinder, and pour out a solid 
granular secretion which immediately hardens to form the basis of 
the central stylet. 
The cells of this cylindrical mass are at first without any very 
definite arrangement, so that the first indication of the basis is a 
solid rod of secretion without definite shape. Gradually, however, 
the secreting cells (pi. 25, fig. 20-25) assume very definite positions 
and are arranged around a lumen of characteristic shape, thus 
making a mold in which the secretions harden to form a stylet 
basis of exactly the same proportions. The mold is at first very 
narrow, so that primarily the basis is slender, cylindrical, and very 
small. 
The great diversity in the shape of the basis in different species 
of Hoplonemertea is thus dependent upon the arrangement of the 
cells forming the mold into which the secretion that forms the basis 
is poured. 
The basis increases in size with the accumulation of secretion and 
gradually acquires the definite form characteristic of the adult. 
Even in a nearly mature embryo, however, the basis is still much 
more slender and of vastly smaller size than in the adult. A com¬ 
parison of the diameter of the basis of an adult worm with that of 
an embryo still in the body, but nearly mature, is represented in 
figure 1), the larger circle representing the outline of the basis in 
the proboscis of the adult, and the 
much smaller circle in the center of 
the large one, a similar outline in the 
embryo. The relative diameters are 
about as 1 to 10, thus corresponding 
with a comparative cross section of 1 
to 100. The basis is, however, much 
more slender in the embrvo than in 
the adult, the relative lengths being 
about as 1 to 4 or 5. The actual bulk 
of the basis in the adult is therefore 
not far from four or five hundred 
times that of the corresponding part 
in the mature embrvo. 
The cylindrical outgrowth of cells which secrete the basis takes 
place from the wall of a conspicuous chamber (pi. 25, fig. 20) in 
Fig. D.—Diagram showing compara¬ 
tive size of cross sections of basis 
of central stylet in the adult worm 
(outer circle), and in a nearly ma¬ 
ture embryo (inner circle); both 
drawn to the same scale, x 567. 
