8 Papers from the Marine Biological Laboratory at Tortugas. 



isthmus of connecting tissue was far too narrow to permit of any consider- 

 able interchange of circulatory or nutrient fluids between the two medusae. 

 In experimenting with circuit -waves in ring-shaped strips of sub- 

 umbrella tissue of Cassiopea or Stomolophus it is often desirable to be able 



to direct the course along which the wave 

 shall travel. 



This can be accomplished if a slight mo- 

 mentary pressure, such as the touch of a finger, 

 be brought to bear upon the ring near the 

 point of stimulation and opposite to the direc- 

 tion in which one desires the wave to travel. 

 Thus in fig. 2 the star (*) marks the point at 

 which the ring is to be stimulated, while the 

 dotted area marks the pressed place, and the 

 arrow shows the direction of the resulting 



FIG. 2. Method of determining 



direction of a wave of con- wave which will continue to travel around 



and around the ring. That half of the initial 



wave which proceeds to the pressed place is so much dampened and 

 reduced by the poorly conducting tissue of the pressed area that the 

 wave in the opposite direction annuls it when they meet. 



DETAILS OF EXPERIMENTS. 



PART I. 

 NEURO-MUSCULAR MOVEMENTS. 



An extensive series of observations was carried out upon the effects 

 of the cations sodium, magnesium, potassium, and calcium upon the 

 neuro-muscular movements of Lepas and of Annelid worms at Tortugas. 

 The Annelids experimented upon were several common species of Euni- 

 cidas found in the crevices of coral rock, among them being the Atlantic 

 palolo worm Eunice fucata. I also made use of several forms of Nereis. 



The sea-water at Tortugas is well imitated for physiological pur- 

 poses by a van'f Hoff's solution consisting of looNaCl + 7.8MgCl 2 + 

 3.8MgSO 4 + 2.2KC1 + 2.5CaCl 2 , all of 0.625 molecular concentration. 

 The Atlantic palolo Eunice fucata will live for over three weeks in this 

 solution in an apparently normal condition. How much longer it might 

 have survived I can not state, but the worms appeared to be normally 

 active when the experiment was terminated; indeed, the worms and 

 Lepas lived better in the artificial than in natural sea-water in aquaria 

 under similar conditions in the laboratory. This I attribute to the purity 

 of the Kahlbaum salts and of the distilled water used in making the 

 artificial sea -water, and its consequent freedom from bacteria. It is 

 remarkable that, contrary to Bethe's 1 experience in maintaining Rhiz- 

 ostoma pulmo alive in artificial sea-water at Naples, I found that the 

 addition of a slight amount of CaCO 3 was not necessary and that it 

 did not appear to improve the life-sustaining powers of the van't Hoff's 

 solution. It produced, however, no injurious effect. 



1 Bethe, 1908, Pfliiger's Archiv fur ges. Physiol., Bd. 124, pp. 54i~577- 



