
As the egg enters the oviduct, a series of divisions 
is proceeding at a rapid rate. Nelson and Segal (1958) working 
with rats found that a triphenyl ethanol derivative MER=25 pre- 
vented the further development of the zygote as it moved down 
the oviduct. Twenty-five mg. per kilo body weight was given 
orally to female rats for 4 days after the first sperm was de- 
tected in the vagina. Implantation was prevented in all cases. 
The substance is believed to act rapidly on the ova after the 
extrusion of the second polar body, and it is believed to be 
secreted directly into the lumen of the oviduct and there act 
directly on the egg. MER=-25 was found to have no effect after 
implantation. 
Another stage at which inhibition has been demonstra- 
ted, again not in avian species, is the blastula stage of de- 
velopment. Brachet (1958) demonstrated that Bemercaptoethanol 
inhibited cleavage by inhibiting cell division. The compound 
is suspected to act as a reducing substance on the <-SH 
linkages of the amino acids involved in the protein build-up 
necessary in cell division. Embryogenesis has been described 
chiefly by Weiss (1948). “An embryo is built like an auto- 
mobile, on an assembly line by innumerable processes succeeding 
each other--some with a latitude for repairs, others not. At 
any one point along that complicated line, some agent which we 
apply may strike. Sometimes it strikes at a time we apply it 
and sometimes later, because of a latency of its actions.” 
Inhibition is described as the restraining of, or 
the cessation of, or the interference with, the function of an 
organ or agent. This may be at a specific tissue or cellular 
area or at some more general area, At any time in the develop- 
mental stages of the chick from the embryo to the mature chick- 
en,. the expression of lethal genes may take place. Here, the 
definition of embryogenesis is somewhat extended to take in the 
delayed action lethal recessive, 
2. Genetic lethal factors. 
The first lethal mutation in poultry was reported by 
Dunn (1923). The Wyandotte lethal as it was termed was found 
to reduce hatchability to 30 per cent. Since then, a wide range 
of lethals has been reported which have been summarized by 
Landauer (1951). Subsequently, several new lethal mutations 
have been reported. 
Bernier (1954) reported a dominant lethal in Single 
Comb White Leghorns. This is an obligate lethal which affects 
the chicken at 1 to 4 days; circulation is not properly 
established. 
The Sparrow Head lethal was reported in New Hampshire 
chickens by Gyles, Gilbreath and Smith (1953). This is a de- 
layed lethal recessive which produces a distinct shortening of 
the head bones and beak at 9 weeks to maturity. 
37 
