ANDREWS: ANNULUS VENTRALIS. 
435 
median groove seen in figure 1 (pi. 43), and the two elevations right 
and left of it are the tuberosities in nearly vertical section. The 
transverse bridge that lies between the cavity of the vestibule and the 
exterior in this section, text-figure C, is a section of the spur seen in 
figures 1 and 5 (pi. 43), passing over from the right tuberosity to end 
under the left tuberosity. 
The actual orifice leading from outside into the vestibule of the trum¬ 
pet is variable and also difficult to see on account of the overhanging 
of the tuberosities and the spur. As indicated in white in figure 7 
(pi. 43) it is a crescentic aperture with its concave side more or less 
encroached upon by the spur from the right tuberosity. The large 
cavity of the vestibule is there represented by the long light area 
leading off from the crescentic orifice to the right. The dark line 
bounding the orifice in the figure represents the optical section of the 
chitinous covering of the exoskeleton which dips in at the orifice to 
line the interior of the whole trumpet. To the right this dark bound¬ 
ing line is continued to represent the commencement of the zigzag 
suture. r 
The cavity of the trumpet communicates with the surface not only 
by the above open orifice but by a continuous bent slit that comes to 
the surface as the above zigzag suture represented in figures 1 and 5 
(pi. 43). The sides of this slit are so nearly in touch with one another 
and the suture is so nearly a closed one that this long continuous open¬ 
ing of the trumpet can be made out only with difficulty in the natural 
state though in dried and shrunken section material it is quite evident. 
The nature of this connection of cavity and surface may be made out 
from such sections as figures 11 and 14 (pi. 44). The former repre¬ 
sents a vertical longitudinal section much like that shown in the cen¬ 
tral part of text-figure B. The ventral side is uppermost and the 
anterior face is the sloping one on the right. The cavity is cut across 
as four spaces and in three of these there is patently a slit leading out 
to the surface, but the fourth, most to the left, is the most ventral ter¬ 
minal pouch or recess and it opens into a common slit leading to the 
surface from the third space. The bounding dark line represents 
the clear chitinous layer that covers the entire exoskeleton and passes 
in at each slit to line all the internal cavities in the exoskeleton of the 
annulus. The more vertically striated, external layer of the exoskele¬ 
ton is continued as the striated lining layer of the trumpet while the 
thicker inner laminated layer of the exoskeleton is continued as the 
