484 A. W. BELLAMY 
The conditions under which recovery will occur to a suff.cient 
degree to reveal a marked differential are necessarily some- 
what exacting. The strength of the solution (if a chemical sub- 
stance is used), the length of exposure, and the physiological 
condition of the embryo must all be taken into consideration. 
If the conditions are too severe, recovery will not take place at 
all. Furthermore, the relation between different regions of the 
physiological axes of the developing organism, as regards rate or 
degree of activity, is continually changing. During early cleav- 
age stages the apical pole represents the region of greatest 
activity as measured by rate of cell division, concentration of 
protoplasm, etec., and is most susceptible to a variety of external 
agents and conditions. Later the dorsal lip of the blastopore 
arises, probably by physiological isolation,? as a secondary 
region of high susceptibility.‘ In fact, this secondary or posterior 
growing region is at the time of its appearance and for some time 
afterward quite as or even more susceptible than the apical region. 
Apparently it represents during this time the most actively grow- 
ing region of the embryo. Hence the physiological condition of 
the embryo at the time of exposure to the inhibiting conditions 
and at the time of removal from them, as well.as the severity of 
the conditions, must play an important part in determining the 
rate and extent of development of those regions emphasized in 
recovery after removal from the inhibiting conditions. 
It is usually a great satisfaction to the reader to have before 
him the complete records of experiments of this nature, but since 
the chief purpose of this report is to direct attention to the 
fundamental similarity of teratological forms however produced 
and to offer a physiological interpretation of the data, and es- 
pecially since many of the essential facts of abnormal develop- 
ment in the frog have been recorded by a considerable number of 
3 See Bellamy, 719, pp. 349, 350. 
4The at least temporary independence of the dorsal lip region is further 
indicated by certain of Spemann’s (718) recently published experiments. Taking 
two triton eggs at the beginning of gastrulation, he removed and exchanged 
between the two eggs the entire animal pole cap of cells, at the same time rotating 
them through 90°. In these cases he found the anterior end of the medullary 
plate developing in apposition to the posterior end of the lower half of the egg. 
