46
MICHAEL LOCKE
aries. As the taenidia enlarged further to form the final pattern, the
plasma membrane moved back towards its original shape, as a fairly
smooth-walled cylinder. There was nothing in the formation of the
pattern in tracheae or tracheoles which conflicted with the hypothesis
that they are produced primarily by the expansion and buckling of the
cuticulin.
mm
A
B
c
D
FIG. 11. Diagram summarizing the formation of the cuticulin of the surface
cuticle. A: Cuticulin appears at the tips of microvilli. The edges of the patches of
cuticulin are connected to the plasma membrane by wisps of material. B: The
cuticulin completely covers the surface, but continues to grow. C: The patches of
cuticulin become larger and more convex until D: The final pattern of large
rounded tubercles is formed.
In the surface cuticle of both kinds, profiles of the cuticulin layer
appeared as dense lines at the tips of microvilli (Fig. 11). It then
extended in tiny convex patches over several microvilli, but with the
edges most commonly over a tip. The edge, believed to be a growing
point, was often connected to the microvilli by wispy bridges of diffuse
material. The patches of cuticulin became more and more convex as