MODIFICATION OF DEVELOPMENT IN THE FROG 493 
Potassium cyanide 
Eggs in a two-cell stage at the beginning of the experiment (experi- 
ment KNC-C.9°). The eggs were divided into two lots and treated 
as follows in m/10,000 KNC: 
Lot A. (a) 48 hours in KNC. Equatorial gastrulation beginning 
in a few eggs. Control eggs show advanced yolk plug stages. 
(b) 4 days in KNC. More than 90 per cent of the eggs 
show a circular blastopore following the equatorial region (equatorial 
gastrulae). The controls are now elongating embryos with heads 
formed. 
(c) 5 days in KNC. Little if any change. The eggs con- 
tinued in this solution without further advance in development until 
the eighth day, when they began dying in considerable numbers. 
Lot B. (a) 4 days in KNC, plus 2 days in water. Mostly neural 
fold stages with relatively small head region and showing a persistent . 
yolk plug. Figures 10, 11 illustrate one of the less extreme embryos 
of this type. Most of the embryos show a much larger yolk plug and 
situated more dorsally and also showing greater inhibition of the head 
region. Comparison with figure 55 reveals a striking resemblance in 
the type of abnormality produced with the aid of two widely different 
chemical agents—potassium cyanide and lithium chloride. 
(b) 4 days in KNC, plus 5 days in water. Mostly micro- 
cephalic forms showing spina bifida and with persistent yolk plugs. 
All of the embryos show various degrees of approximation to complete 
‘fusion’ of ventral suckers and olfactory pits. Figure 23 illustrates 
one of these embryos. It will be noticed that the yolk plug is situated 
dorsally and that the two tails curve upward with the distal ends di- 
‘rected toward the anterior end. 
(c) 2 days in KNC, plus 8 days in water. Spina bifida of 
various sorts. Figure 66 illustrates one of these, showing in addition 
a microcephalic condition and a single ventral sucker. This is repre- 
sentative of the lot at this age and resembles somewhat the embryo 
illustrated in figure 23. Figures 67, 68 are later stages of the few less 
extremely modified embryos drawn to the same scale. Figure 68 is a 
ventrolateral view of one showing the ventral suckers almost completely 
‘fused’ and a single olfactory pit. Probably 5 per cent of the embryos 
in this lot were similar to 67, 68, the remaining embryos approximating 
the type shown in figure 66. 
This experiment is typical of those furnishing conditions mentioned 
at the beginning of the description of the experiment. The range of 
concentrations of KNC that will produce considerable deviations from 
the normal and still permit development to proceed beyond gastrula 
stages is rather limited. In m/1000 development stops in mid-cleavage 
stages with the pigmented and unpigmented cells approximating the 
same size. Likewise in m/5000 development stops during cleavage 
6 Citations of experiments in italics refer to those done by Professor Child in 
1916. 
