306 
Studies on Pedicidus 
cepulatory apparatus is retracted within the male’s body, the rods 
approach each other leaving but a narrow sht between them distally, 
the interspace broadens considerably behind; it is through this space 
that the penis issues (PI. Ill, fig. 1, DU. cl.). The dilator, when at 
rest, as shown in the figure just mentioned, points backward and shghtly 
dorsally within the animal, lying on a plane with the basal plate. The 
point of the dilator is slightly curved ventrally (the reverse when 
seen in copula). The dilator rods are stoutest basally, they become 
flattened dorso-ventrally as they approach the tip; they show longi¬ 
tudinal ridges, and near their bases carry a lateral, backwardly directed 
spine. The supposedly composite origin of the dilator from the 
parameres -i- endomeres of Cummings has been already referred to 
[vide p. 299). 
When, as we shall see presently, the process of copulation begins, 
the first part of the apparatus to appear is the dilator (Text-fig. 5); 
it is flexed upon the basal plate at about a right angle. At the next 
stage the vesica is slightly everted and the basal plate protrudes slightly. 
The pressure exerted by the vesica and penis in being forced through 
the cleft of the dilator greatly enlarges the cleft. The union at the 
distal end of the dilator, however, limits the increase in the space, and 
owing to the shafts becoming flatter and weaker as they progress toward 
the point they yield to the pressure and become twisted out of shape to 
a greater or less degree as depicted in PI. Ill, fig. 2. 
It should be noted that the vesica, described below, is in continuity 
with the upper inner margin of the cleft portion of the dilator, and to 
some extent perhaps with the basal plate. The boundary formed by 
the margin of the cleft about the issuing vesica may be likened to the 
edge of a pipe-bowl which is continuous in contour with a soap bubble 
blown from it. In addition, when the dilator is extruded and flexed, 
what was previously the dorsal having now become the ventral surface, 
a delicate collar-like sheath becomes visible, extending upward out of 
the genital orifice and fusing with the under surface of the dilator; 
this sheath forms a tube through which the vesica and penis ghde 
outward from the body. The structure is best seen in Text-fig. 5; see 
also Text-fig. 2 and PI. Ill, fig. 2. 
(3) The vesica penis, when retracted into the body, carries with it 
the sUitunten penis and penis, all of which come to lie dorsally upon 
the hollow of the basal plate as in a spoon (PI. Ill, fig. 1). The teeth 
which stud the outer surface of the extruded vesica now appear internal 
(Text-fig. 3), and the walls of the vesica are thrown into numerous folds 
