:U6 (summary of current researches relating to 



the interstitial protoplasmic network inside the embryo. This line of 

 investigation is obviously of great importance, for as we come to know 

 the properties of individual cells indetail.it will be possible to form 

 an accurate conception of the influences actually at work in Bhaping the 

 embryonic body. 



Lymph Hearts of Chick Embryos.* — Eleanor Linton Clark and 

 Eliot Iu Clark have studied the pulsations of the posterior Lymph hearts 

 in chick embryos and their relation to the body movements. The pulsa- 

 tion first appears in embryos of six to seven days (19-22 m.m.), and at 

 this earliest stage is intimately connected with the periodic movements 

 of the embryo. Lymph heart contractions accompany the periodic 

 spasms and never occur in the interval between body movements. Each 

 beat is invariably accompanied by a contraction of the tail. AVhen the 

 body movements are paralyzed by chloretone, the lymph heart pulsations 

 also cease. 



In successive later stages there is a gradual increase in the inde- 

 pendence of the beating lymph heart. First, the pulsations become 

 dissociated from the tail contraction, although still occurring only during 

 the periods of body movements. Then there is a series of stages in 

 which the lymph heart contracts more and more frequently during the 

 period of rest, although still beating a number of times during each 

 spasm. When chloretone is added, at these stages, a larger number of 

 single pulsations occur independently, at irregular intervals. At these 

 stages, the lymph heart is capable of entirely independent function, but 

 is influenced in its rhythm by the periodic spasms of body movements. 



Finally, a stage is reached in which the lymph hearts are unin- 

 fluenced, in any way, by the body movements. During all of these 

 stages, mechanical stimuli, such as pressure over the surface with a fine 

 needle, or direct puncture of the myotomes, failed to influence the body 

 movements. Although the lymph heart does not respond to pressure 

 over the surface, it always contracts when its wall is actually pierced. 

 At the stage in which the lymph heart is not yet independent, such a 

 puncture instigates tail contractions along with the lymph heart pulsa- 

 tions, while at later stages it stimulates the lymph heart alone. 



The authors were unable to come to a decision in regard to the 

 structural connexion between the lymph heart and the body muscula- 

 ture. They suggest four possibilities and discuss them :—(l) that thi 

 lymph heart musculature is derived from the myotomes, and that there 

 i> for a time a connexion between the two : (2) that the muscle of the 

 lymph heart is temporarily supplied by the same nerves which supply 

 the myotomes ; (3) that the lymph heart is merely stimulated mechanic- 

 ally by the contraction of the adjacent muscles ; and (-4) that, at first, 

 the contractions of the lymph heart result from the same stimulus which 

 brings about the periodic body movements, and that this stimulus is 

 gradually subordinated to the stimulus caused by the increasing amount 

 ol' lymph, brought to the lymph heart by the lymphatic vessels from the 

 fast-growing allantois and from the posterior half of the chick. 



* Journ. Exper. Zool., xvii. (1914) pp. 373-94 (2 charts). 



