EARLY PULSATIONS OF LYMPH HEARTS 383 



account by these observers, must be quite considerable, since, accord- 

 ing to our observations, chicks of six days move very actively, approxi- 

 mately one quarter of the time, a total of six hours out of the twenty- 

 four, chicks of nine days, one-third of the time or eight liours out of the 

 twenty-four, while up to the thirteenth or fourteenth days the time of 

 the movements increases still further. 



Harrison, on the other hand, has made a significant beginning at 

 studying the relation between muscular movement and the develop- 

 ment of muscles and bones. He found that muscles differentiate rela- 

 tively normally in tadpoles whose movements are prevented by the use 

 of chloretone, as well as by the removal of nerves. He also observed 

 that ossification occurred in the hind limb of a tadpole into which no 

 nerve had grown, and hence in which there was no muscular movement. 



In a new-born calf E. H. Weber found total absence of the spinal 

 cord and nerves below the first thoracic vertebra. Corresponding to 

 the absence of nerves, the muscles were entirely absent, in the pos- 

 terior part of the body, and while the bones of the hind limb were 

 present and described as 'normally developed' yet the hind limbs weighed 

 only one-half as much as the fore limbs, no description is given of their 

 architecture, and all the joints were ankylosed. Between these two 

 sets of observations there is a wide gap in which it remains to be deter- 

 mined to how great an extent the muscular movements in embryos regu- 

 late the development of the typical architecture of bones, the form of 

 joint surfaces and the growth of muscles. 



THE PULSATION OF THE LYMPH HEART 



In our observations of the pulsation of the lymph heart, in 

 chicks of various stages, we kept careful records of the exact 

 time at which each spasm of muscular movements commenced, 

 the length of the interval between movements, and the number 

 of lymph heart beats occurring during the observation. 



As already stated, in chicks of 5 to 6 days, the region in the 

 angle of the pelvis and tail, later occupied by the lymph heart 

 contains a plexus of lymphatic capillaries filled with stagnant 

 blood. At this stage, the movement of the tail from side to 

 side, at the time of each periodic spasm of body movements, is 

 violent enough to cause a blanching of this whole region, par- 

 ticularly noticeable in the superficial blood capillaries. But the 

 definite localized contractions so characteristic of the beating 

 lymph heart of later stages, are not yet present. 



Stage 1. In embryos of 6 to 7 days (measuring from 19 to 

 22 mm. greatest length, before fixation) the stagnant blood is 



