170 RAYMOND BINFORD 
to form the wall of a structure many times larger than the cap- 
sule. The central body must also be considered as one of the 
structures taking a part in the explosion of the capsule. We have 
therefore three changing structures, a swelling mass, a stretching 
membrane, and an elongating bod each of which take a part 
in determining the form of the inversion. To these must be 
added two structures which do not change and are resistant in 
their nature. These are the wall of the capsule and the collar 
surrounding the hole in the capsule, through which the tubule 
is everted. Let us now follow the interaction of the forces in- 
volved in the behavior of these changing structures. For this 
purpose we shall divide the explosion into four stages. 
Stage 1. The eversion of the outer cavity of the tubule (fig. 67). 
Two forces probably take part in this, the pressure in the capsu- 
lar cavity and the elongation of the central body. 
Stage 2. The elongation of the everted outer cavity (figs. 68 to 
71 and 76). This results in the formation of the collar (fig. 
68, r.). Here again two forces may be involved, the swelling of 
the material in the capsular cavity and the further elongation 
of the central body which stretches the portion of the inner 
tubule which bounds the inner tubular cavity. The fact that 
the everted portion is sometimes longer in the axis through which 
the central body passes, indicates that this body may be exerting 
an out-pushing force. If this be the case, we have here an elastic 
body which has become active by being released from compres- 
sion; that is, the central body elongates like a. coiled spring. 
This action is fully discussed by Koltzoff. The pressure in the 
capsular cavity is sometimes shown by the squeezing of the 
central body out through the outer end of the tubule when it 
has lost its resistant properties. 
Stage 3. The second eversion of the inner tubule ( figs. 77 to 79). 
From the condition shown in figures 71 and 76, the increasing 
pressure in the capsular cavity causes the wall of the everted 
tubule to swell to the form shown in figure 72. Finally, the 
pressure becomes so great that the ring which formed the division 
between the inner and outer tubular cavities (fig. 61, 7.t.c. and 
0.c.) gives away and a part of the tubule bounding the inner 
