432 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
narrow bent tube we will call the trumpet tube and the small rounded 
posterior sac that ends the cavity will be called the recess. In a stained 
frontal section of the exoskeleton of the annulus (pi. 43, fig. 6) the 
very thick walls of the trumpet have an inner lining of chitinous 
material, not here seen, and are made of an inner darkly stained layer 
and a thick outer layer. This outer layer on the level of this par¬ 
ticular section is continuous right and left with the rfiaterial of the 
bottom of the transverse depression of the annulus, while anteriorly it 
is continuous with the material that forms the rim all round about 
the annulus. The two large spaces right and left are the portions 
of the annulus that descend as the cavities within the tuberosities and 
they are filled by connective tissue and lined by epidermis. This is 
also true of the small median space posterior to the trumpet cavity 
in the figure. This space is the deepest part of the posterior trans¬ 
verse groove of figure 2 (pi. 43), that is, part of the promontory 
of figure 1. The trumpet cavity in figure 6 (pi. 43) shows anteriorly 
the wide vestibule passing from left to right and then the narrow 
and bent^tube which in this section ends abruptly but in lower sec¬ 
tions was followed downward as the terminal enlargement or recess. 
The cavity of the trumpet is thus bent not only from right to left 
but up and down in a vertical plane so that the posterior termination 
is much below its general course, as is well seen in text-figure B. 
This is a view of a median vertical section through the entire annulus 
and the parts anterior, posterior, and dorsal to it. The exoskeleton 
is represented in black and the part of it belonging to the annulus is 
the downward projecting part containing three small holes, two of 
which open below to the exterior by slits. Dorsal to the exoskeleton 
is a mass of connective tissue, full of cavities, in life containing blood, 
and this connective tissue is everywhere covered bv epidermis where 
it comes near the exoskeleton. Passing from side to side in the figure 
is the part of the slender sternal artery and this is connected with the 
descending artery near the middle of the figure. This descending 
artery is slightly indicated passing up to the right of a large venous 
space. Most dorsally in the figures are the median nerve-cord and the 
ganglia of the second, third, and fourth somites of the thorax (counting 
from anterior which is right-in the figure) and the ganglion of the fifth 
thoracic somite, lying far to the left in the figure. It will be seen that 
the nerve cord connecting the ganglion is interrupted where the de¬ 
scending artery and vein pass, and other sections show the nerve-cord 
as a ring around these vessels. 
