EARLY PULSATIONS OF LYMPH HEARTS 377 



embryo becomes a gentle swaying and, in later stages, all move- 

 ment is absent. Preyer showed that the amniotic contractions, 

 contrary to the ideas of von Baer and Remak, were not caused 

 by the cold air, but were normally present in warm eggs and 

 ceased a short time after exposure of the egg to cold air. 



Preyer's method enabled him to keep the embryos alive and 

 active for only a short time after opening the shell. By making 

 use of the warm chamber and the binocular microscope, we have 

 been able to watch the passive and active movements of the 

 chick for several hours after opening the shell, and to study them 

 in greater detail. We found that the amniotic contractions fol- 

 low each other in rapid succession: each peristaltic wave con- 

 sumes on an average, 3.3 seconds, and about 4.5 seconds elapses 

 between the cessation of one wave and the beginning of the 

 next one. We also observed, in a five-day chick, four distinct 

 types of amniotic contraction: (1) The peristalsis starts at the 

 top of the head and passes completely down to the tail of the 

 embryo; (2) The contraction starts at the same place but ex- 

 tends only half as far, i.e., to the posterior edge of the wing; (3) 

 The wave starts over the neck bend, half way between the ear 

 vesicle and the anterior edge of the wing and extends simul- 

 taneously in both directions; (4) The contraction wave starts 

 posteriorly and extends from the tail to the head end of the 

 embryo. Types (1) and (4) were found to occur most frequently, 

 and in type (1) the passive movement of the whole embryo was 

 the greatest. With this type there is evidently a rapid circula- 

 tion of the amniotic fluid for as the contraction wave passes 

 posteriorly, the fluid is squeezed out and the amnion comes in 

 contact with the embryo, and the amount of fluid increases in 

 the relaxed part of the sac. The extremities are pressed tightly 

 against the body wall, as the amniotic wave passes over them. 

 This undoubtedly has an effect on the form of the chick, for in 

 embryos which had lived for several hours with the amnion 

 removed, we noticed that the extremities, on the side away from 

 the yolk, showed a tendency to grow away from the body until 

 they often projected at right angles to it. 



