
RECENT FINDINGS IN THE INHIBITION OF AVIAN EMBRYOGENESIS 
Macreay J. Landy 
1. Normal sequence of embryogenesis. 
Embryogenesis is in progress as the zygote moves 
down the oviduct and finally appears on the outside. Fertiliza-~ 
tion usually takes place in the infundibulum of the female as 
was first noted in studies with the pigeon (Patterson, 1910). 
However, fertilization may take place as soon as the germinal 
disc is exposed by rupture of the follicular wall. Normally 
15 minutes elapses between ovulation and the entrance of the 
sperm (Romanoff, 1960). 
As the sperm and egg come into close proximity, vari- 
ous substances recognized only as fertilizins, antifertilizins, 
agglutinators, etc. are secreted by sperm and egg alike. These 
substances have been studied extensively in the sea urchin. 
aoeee substances interact to inhibit or facilitate sperm pene~ 
tration. 
The vitelline membrane surrounding the ovum is pene- 
trated by the sperm or by many sperms. As many as 25 separate 
sperm have been counted in the vitelline membrane (Harper, 1904). 
The sperm enters the germinal disc and the second maturation 
division of the egg nucleus proceeds to completion. A reduce 
tion division occurs with the formation of the second polar 
body, and either at this time or at the second maturation 
division metaphase stage, fertilization is said to take place. 
The male and female pronuclei are formed. As the 
zygote travels down the oviduct carried by peristaltic move- 
ments, the formation of the segmentation nucleus takes place. 
Here, in the oviduct, the ovum is invested with several layers 
of albumen. The zygote then travels to the isthmus where the 
shell membrane is laid down. In this area, the first segmenta- 
tion division takes place. Next, the calcareous shell is 
secreted around the zygote. Meanwhile, the development has 
proceeded to the multicellular stage with the formation of the 
secondary germinal layer during cleavage. 
Gametogenesis and fertilization are necessary pre= 
cursors to embryogenesis. At any point during this sequence, we 
might interrupt or interfere with the processes going on and 
thus prevent or delay the next step. 
At the sperm-egg interaction level, the structure of 
the ovum is important. It is at this stage that there is an 
interaction of substances termed fertilizins, lytic agents, etc. 
In the sea urchin and the ares these processes are an antigen- 
antibody type reaction. 
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