1390 Journal of Applied Microscopy 



normal beat. The motor stimulus which causes the rhythmical pulsation must 

 arise in the muscles of the heart itself, since a very careful search with a great 

 variety of histological methods failed to reveal either ganglion cells or nerve fibers 

 in this organ. 



The next general subject considered, is the cause of the periodical change 

 in the direction of the blood flow and the heart beat. After a critical review of 

 the theories which have been advanced by previous workers, Schultze proceeds 

 to an account of his own explanation. By isolating one end of the heart he 

 found that its activity showed a marked periodicity. There were periods of maxi- 

 mal activity, in which the pulsations were strong and rapid, followed by periods 

 of minmal activity during which the beats were weakened and nearly dis- 

 appeared. Both ends of the heart, under normal circumstances, would, of course, 

 show this periodicity. From the fact that any single muscle fiber of the heart 

 cannot be made by extra stimulation to further react when already contracted or 

 nearly contracted, together with the fact that the stimulus is conducted in the 

 muscle fibers themselves, it is shown that the end of the heart which is beating 

 more rapidly and strongly will determine the beat of the whole. Taking this in 

 connection with the periodicity in the activity of either end of the heart, the 

 result is that first one and then the other end will determine the beat of the whole 

 heart. When, for example, the abvisceral end is in its period of maximal activity 

 it will set the whole organ to beating synchronously with it, outweighing and 

 obscuring the weaker pulsations of the advisceral end. After a time, however, 

 its period of maximal activity ends and that of the opposite end begins and con- 

 trols in turn the beat of the whole. The continuation of this process results in 

 the observed alternation in the direction of the heart beat and blood flow. 



R. p. 



RadI, Em. Ueber den Phototropism einiger This paper gives an account of the effect 

 Arthropoden. Biol. Centralbl. 21 : 75-S6, of light on the movements of the eyes 



of various Cladocera, and the relation 

 of these eye movements to the phototaxis of the organisms. It was found that 

 sudden shading of a Daphnia caused an immediate drawing in of the eye stalks. 

 Careful study showed that under all conditions the eye was directed towards the 

 source of greatest illumination. If, for example, a Daphnia on a slide on the 

 microscope stage be shaded by the hand from above, the eye stalk will be rotated 

 so as to point its tip towards the opening in the diaphragm ; while, on the other 

 hand, if the light be diminished from below, the eye will turn up towards the 

 light now coming from above. When the organism (Daphnia) is oriented with 

 its back towards the light the eye is in its normal position, with all the muscles 

 of the stalk in a state of equal tension. If now the preparation is turned so as 

 to bring the animal out of its position of orientation, it is found that the eyes 

 maintain their orientation while the body turns about them as a fixed point until 

 it is again in a position such that the eye muscles are in a state of equal tension. 

 These reactions of the eyes do not usually appear in strong, direct sunlight, there 

 being apparently an upper limit of intensity beyond which the normal phenomena 

 do not appear. 



Observations were made on the method of orientation to light of specimens 



