37G E. L. CLAEK AND E. R. CLARK 



Von Baer observed movements in chicks of five daj^s which 

 he beheved to be due to the exposure of the embryo to the cold 

 air. On the seventh day he states that the movements have 

 become more general: ''Der Embryo schwingt in Amnion hin 



und her, auf dem Nabel, wie auf einem befestigten Stiele Es 



schien mir daher eine Art unregelmassiger Pulsation im Amnion." 

 Von Baer found that the contractions of the amnion were very 

 active in chicks of eight or nine days and that after that time 

 they became weaker. 



The subject of amniotic contraction was further investigated 

 by Remak in 1854. After opening the egg, he noticed violent 

 wave-like movements of the amnion, which were now and then 

 followed by quieter rhythmical contractions. When the con- 

 tractions ceased they could be started again by pricking the 

 amnion with a needle. Pieces of amnion, examined under a 

 simple lens, were found to contract when stimulated. Remak 

 found smooth muscle fibers in the amnion, which increased in 

 abundance up to the tenth day of incubation; after this time 

 their number diminished. Nerves, according to Remak, are not 

 present in the amnion. Like von Baer, Remak doubted the 

 presence of these peristaltic contractions in normal embryos 

 inside the egg, and stated that the violent contractions were 

 probably caused by exposure to the air. 



This last point was refuted by Vulpian in 1857, who observed 

 the embryo in unopened eggs held before a bright light. He 

 saw the swaying movement of the embryo in chicks of five to 

 eight days and found it to be violent and continuous in the 

 unopened eggs, under normal conditions. He also described con- 

 traction of the under surface of the allantois in chicks of twelve 

 days and over. 



Preyer in 1885, studied these contractions of the amnion, as 

 well as the other type of movements in chick embryos. He 

 studied chicks on each day of their development, by means of a 

 specially constructed ooscope, both before and after opening the 

 shell and found that the amniotic contractions first appeared 

 in embryos of four days, and continued up to the thirteenth 

 day of incubation. At this time, the violent swinging of the 



