PATTERNS IN THE INTEGUMENT OF INSECTS
59
it is possible to perform integumental grafts, sometimes using different
species as markers. In experiments upon the abdomen and upon the
appendages, it was found that the cells of the epidermis are like one
another transversely but differ in the axis in a segmentally repeating
way which could be described as a segmentally repeating gradient of
some kind of difference (Locke, 1959a,b, 1960b, 1964, 1966b). These
experiments are discussed below in Sections II,B,1-10.
1. Grafts in the Abdominal Integument
The abdominal integument in Rhodnius and Triatoma has lent itself
to these skin grafting studies because of the surface pattern. In the larva,
the pattern is one of stellate pleats interspersed between the bristlebearing plaques (Fig. 22). In the adult, the pattern changes to one of
transverse ripples (Fig. 23). The nature of the ripple pattern makes
it ideal for detecting displacements in the axis. I t is relatively easy
to interpret the way in which the ripple lines are displaced and link
up in response to grafting operations. Grafts will take readily with a
marriage of host and graft patterns when displaced laterally (Fig. 25).
There is also no disturbance of the adult pattern when grafts are exchanged between segments, as long as the relative positions within the
segment are the same. However, when the relative positions are altered
in the axis within a segment, either by transposition (Fig. 26) or by
rotation through 90° (Fig. 27) or 180° (Fig. 28), the adult pattern is
distorted so that the transverse lines of ripples maintain continuity with
others of the same level. From these experiments, we can say that the
epidermal cells are arranged in a segmentally repeating gradient of some
kind, which we can picture as in Fig. 29, the cells are alike from side
to side but differ axially. The characteristic which varies quantitatively
results in the recognition of position in a linear axial order. When displaced from this order, the host and graft patterns interact in a way
predictable from their relative positions.
2. Grafts Involving Inter segmental Membranes
Grafts involving the intersegmental membranes confirm the hypothesis
in Fig. 29, if the intersegmental membranes are neutral regions with respect to their level in the axis (Figs. 30-33). The patterns resulting from
the grafts were usually those predicted from the interaction between host
and graft, but in some experiments the pattern was of a type to be exGrafts can be exchanged from side to side, either mesial-to-lateral or lateral-to
lateral, without affecting the pattern in the adult. Grafts can also be exchanged
from segment to segment without affecting the pattern, as long as the relative position within the axis of each segment remains unchanged. (After Locke, 1959a.)
59
it is possible to perform integumental grafts, sometimes using different
species as markers. In experiments upon the abdomen and upon the
appendages, it was found that the cells of the epidermis are like one
another transversely but differ in the axis in a segmentally repeating
way which could be described as a segmentally repeating gradient of
some kind of difference (Locke, 1959a,b, 1960b, 1964, 1966b). These
experiments are discussed below in Sections II,B,1-10.
1. Grafts in the Abdominal Integument
The abdominal integument in Rhodnius and Triatoma has lent itself
to these skin grafting studies because of the surface pattern. In the larva,
the pattern is one of stellate pleats interspersed between the bristlebearing plaques (Fig. 22). In the adult, the pattern changes to one of
transverse ripples (Fig. 23). The nature of the ripple pattern makes
it ideal for detecting displacements in the axis. I t is relatively easy
to interpret the way in which the ripple lines are displaced and link
up in response to grafting operations. Grafts will take readily with a
marriage of host and graft patterns when displaced laterally (Fig. 25).
There is also no disturbance of the adult pattern when grafts are exchanged between segments, as long as the relative positions within the
segment are the same. However, when the relative positions are altered
in the axis within a segment, either by transposition (Fig. 26) or by
rotation through 90° (Fig. 27) or 180° (Fig. 28), the adult pattern is
distorted so that the transverse lines of ripples maintain continuity with
others of the same level. From these experiments, we can say that the
epidermal cells are arranged in a segmentally repeating gradient of some
kind, which we can picture as in Fig. 29, the cells are alike from side
to side but differ axially. The characteristic which varies quantitatively
results in the recognition of position in a linear axial order. When displaced from this order, the host and graft patterns interact in a way
predictable from their relative positions.
2. Grafts Involving Inter segmental Membranes
Grafts involving the intersegmental membranes confirm the hypothesis
in Fig. 29, if the intersegmental membranes are neutral regions with respect to their level in the axis (Figs. 30-33). The patterns resulting from
the grafts were usually those predicted from the interaction between host
and graft, but in some experiments the pattern was of a type to be exGrafts can be exchanged from side to side, either mesial-to-lateral or lateral-to
lateral, without affecting the pattern in the adult. Grafts can also be exchanged
from segment to segment without affecting the pattern, as long as the relative position within the axis of each segment remains unchanged. (After Locke, 1959a.)