ANDREWS: ANNULUS VENTRALIS. 
469 
(pi. 48, fig. 47) shows the rounded posterior face as it were fallen 
down in the middle to make a median valley on its ventral side. Over 
this median valley passes the suture (pi. 48, fig. 45), to bend off to the 
left and soon to be lost in a deep depressed area far on the left and 
posterior. This depressed area is bounded by a marked rim along 
its left edge while the corresponding region on the right side of the 
annulus is flat and somewhat depressed. 
Seen from the anterior side, the annulus looks like a thin cuticular 
plate, rising up but little and far posterior to its anterior edge. As 
the thin anterior edge of the annulus is continuous with the concave 
sternum of the fourth thoracic somite and only the posterior border 
of the annulus is at all markedly elevated, the whole annulus seems 
to be well fitted to allow the eggs to glide down over it as they come 
from the oviducts on the third legs across the trough-like sternum of 
the fourth somite. The posterior border of the annulus may possibly 
tend to arrest the eggs while they come into contact with the sperms 
issuing out of the suture and then pass on through the median groove 
(pi. 48, fig. 47). But in the absence of actual observations, such 
accurate adjustments of form and functions are extremely hypothetical. 
The dorsal view of the exoskeleton of the annulus (pi. 48, fig. 46) 
shows a small simple tube bending forward to one side and ending 
anteriorly flush with the general ventral surface. 
In translucent preparation (pi. 48, fig. 48), the pocket-like character 
of the trumpet is obvious. The heavy line represents the edge of the 
pocket. To the left this line borders a deep depression (pi. 48, fig. 45), 
which extends posteriorly under the overhanging posterior rim of the 
depression so that a pouch is formed on the left, opening out freely to 
the anterior. To the right there is a similar pouch lying anteriorly 
and opening posteriorly; but its mouth is not open but closed, and 
the heavy lines along the closed posterior mouth are part of the suture, 
which then runs posteriorly and ends on the median line. The open 
pouch on the left is continuous with the closed pouch on the right; 
the former forms the vestibule and the latter the tube of the trumpet. 
The trumpet tube is largely transverse in direction and opens up to 
the surface by curved planes or nearly closed clefts. 
The posterior longitudinal part of the tube is remarkably short and 
simple. It ends on the middle line so that it could discharge through 
the median line of the suture. There was no recess of any kind ob¬ 
served. 
