82
MICHAEL LOCKE
mental membranes, we should expect that grafts isolated with intersegmental membranes should grow preferentially on one side. There are suggestions that this may be the case (Locke, 1960b, plate 6, Fig. 7), but the
experiments have yet to be performed critically with this hypothesis in
mind. The nodes and intersegmental membranes may be alike in being
organizers for growth, but different in their orientation to the gradient
which determines the polarity and hence, the direction of their operation.
The phenomena we should separate would be the gradient, which is an
equilibrium determined by the differential activity of each cell within it,
and the use of the polarity intrinsic in the gradient by the nodes and
intersegmental membranes.
There is a continual need to recognize that the terms used in this
description may have no reality in the phenomena being studied. We can
proceed no further until some structural, physiological, or biochemical
correlation has been made. We should also recognize that the answers
which emerge are going to be complicated. For example, any gradient
resulting from the active transport of charged ions or molecules will set
up a field resulting in a reversed gradient of oppositely charged molecules. The type of hypothesis which deserves to be explored would suppose that the cells in the axis are like lines of leaky batteries increasing
in size, connected with a high resistance in series and a lower resistance
in parallel, the field created being used when necessary to facilitate the
movement of charged molecules important in communication. Coupled
with this we might look for something akin to synapses and presynaptic
vesicles to account for the polarity.
C. Three-Dimensional Patterns Resulting from Cycles of
Activity in Time
1. The Molt-Intermolt
Cycle
The epidermis undertakes a number of syntheses, for the most part
singly, in a temporal succession which determines the composition of
successive layers of the cuticle. These syntheses can be grouped into two
series, those taking place at molting and those in the period between
molts.
The importance of the epidermis at molting, and the success of the
classical experiments in demonstrating the hormonal control of molting,
have resulted in a tendency to ignore the many discrete synthetic events
which make up a molt. Experiments upon hormonal control have been
adequately served by recording the initiation of molting without being
concerned about the synchronization of the syntheses of which it is
composed. The sequence is initiated by the molting hormone, but nothing
is known about the cellular mechanisms for synchronization. Different
MICHAEL LOCKE
mental membranes, we should expect that grafts isolated with intersegmental membranes should grow preferentially on one side. There are suggestions that this may be the case (Locke, 1960b, plate 6, Fig. 7), but the
experiments have yet to be performed critically with this hypothesis in
mind. The nodes and intersegmental membranes may be alike in being
organizers for growth, but different in their orientation to the gradient
which determines the polarity and hence, the direction of their operation.
The phenomena we should separate would be the gradient, which is an
equilibrium determined by the differential activity of each cell within it,
and the use of the polarity intrinsic in the gradient by the nodes and
intersegmental membranes.
There is a continual need to recognize that the terms used in this
description may have no reality in the phenomena being studied. We can
proceed no further until some structural, physiological, or biochemical
correlation has been made. We should also recognize that the answers
which emerge are going to be complicated. For example, any gradient
resulting from the active transport of charged ions or molecules will set
up a field resulting in a reversed gradient of oppositely charged molecules. The type of hypothesis which deserves to be explored would suppose that the cells in the axis are like lines of leaky batteries increasing
in size, connected with a high resistance in series and a lower resistance
in parallel, the field created being used when necessary to facilitate the
movement of charged molecules important in communication. Coupled
with this we might look for something akin to synapses and presynaptic
vesicles to account for the polarity.
C. Three-Dimensional Patterns Resulting from Cycles of
Activity in Time
1. The Molt-Intermolt
Cycle
The epidermis undertakes a number of syntheses, for the most part
singly, in a temporal succession which determines the composition of
successive layers of the cuticle. These syntheses can be grouped into two
series, those taking place at molting and those in the period between
molts.
The importance of the epidermis at molting, and the success of the
classical experiments in demonstrating the hormonal control of molting,
have resulted in a tendency to ignore the many discrete synthetic events
which make up a molt. Experiments upon hormonal control have been
adequately served by recording the initiation of molting without being
concerned about the synchronization of the syntheses of which it is
composed. The sequence is initiated by the molting hormone, but nothing
is known about the cellular mechanisms for synchronization. Different