Atrioventricular Connection in the Turtle. 183 



V-A rhythm produced by electrical stimulation of the atrio- 

 ventricular funnel. In Malacoclemmys geographica the two 

 nerves are not fused into a single trunk, but run separately in the 

 neck just median to the carotid artery. The turtles were decere- 

 brated, and the plastron removed, the circulation being kept 

 intact to a large degree. The vagus was stimulated just above 

 the thoracico-abdominal ganglion, and the sympathetic, between 

 the median cervical and the first thoracic ganglion. 



Stimulation of the vagus nerves alone gave the usual results. 

 The effects of sympathetic stimulation were, however, not so 

 clearly marked. The general effect was a slight augmentation 

 of the auricular contractions. Acceleration of the heart beat 

 was less frequently obtained, the average being from 2 to 3 beats 

 per minute, although an acceleration of as many as 6 beats per 

 minute was registered. 



Conjoint stimulation of the vagus and the atrio-ventricular 

 funnel just below the A-V boundary with relatively strong in- 

 terrupted currents produces a V-A rhythm which lasts over, 

 in different experiments for varying lengths of time, after the 

 stimulation has been discontinued. In these cases stimulation 

 of the vagus nerves with a current of sufficient strength to still 

 the normal heart causes only a decrease in the height of the auri- 

 cular contraction with no effect on the rate of beat. Stimulation 

 of the sympathetic with strong currents stops the funnel rhythm, 

 after which a normal atrio-ventricular beat begins. 



105 (1169) 



Changes in form and position of the retinal elements of normal 

 and transplanted eyes of Amblystoma larvae 

 occasioned by light and darkness. 



By Henry Laurens and J. W. Williams. 



[From the Osborn Zoological Laboratory, Yale University.} 



In order to investigate the changes occasioned by light and 

 darkness in the retinal elements of a Urodele a series of experi- 

 ments on large (37 to 45 mm.) larval and on recently metamor- 

 phosed individuals of Amblystoma was carried out. It was found 



