AUTHOR'S ABSTRACT OF THIS PAPER ISSUED 
BY THE BIBLIOGRAPHIC SERVICE, MAY l 
DIFFERENTIAL SUSCEPTIBILITY AS A BASIS FOR 
MODIFICATION AND CONTROL OF DE- 
VELOPMENT IN THE FROG 
II. TYPES OF MODIFICATION SEEN IN LATER DEVELOPMENTAL 
STAGES 
A.W. BELLAMY 
Hull Zoological Laboratory, The University of Chicago 
SEVENTY FIGURES 
INTRODUCTION 
The fact that it is possible, within limits, to modify and con- 
trol the developmental processes of a wide variety of organisms 
lends weight to the conception that the organism represents a 
complex or ‘pattern’ which, while it is characteristic of the species, 
entails a variety of ultimate ontogenetic possibilities. This or 
that aspect of development is revealed according as the develop- 
ing organisms is exposed to this or that constellation of environ- 
mental factors. Viewed in this light, teratological development 
is simply a consequence of a deviation from the usual trend of 
development. Now, development may be made to depart from 
its usual trend in a variety of ways, and the degree or extent 
of the deviation from the usual course of development seems to be 
limited, for the most part, by two general factors. ‘The primary 
limiting factor is of course the nature of the ‘organismic pattern,’ 
as Child (’20, p. 148) termed it. Since a wide variety of environ- 
mental factors has been used successfully to produce essentially 
similar abnormalities or deviations from the ‘normal,’ the second 
limiting factor would seem to be the intensity! of action of these 
agents rather than any specific action that might be ascribed to 
them. 
1 The word ‘intensity’ is used here in the sense of, e.g., concentration with 
reference to a chemical substance in solution. ; 
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THE AMERICAN JOURNAL OF ANATOMY, VOL. 30, NO. 4 
