PULSATION OF 



Gonionemus, Lepas, Salpa, and the loggerhead turtle. If there be 

 marked differences between the reactions of closely related Scypho- 

 medusse, one may expect even greater disparity between those of ver- 

 tebrates as compared with invertebrates. 



Roman es,L,oeb, von Uexkiill, Hargitt, and others have caused disks 

 to pulsate temporarily by subjecting them to the influence of NaCl 

 solutions, etc., but in all cases more or less toxic effects resulted from 

 the experiments and the sensibility of the sub-umbrella tissues 

 became impaired or destroyed, so that further stimulation soon became 

 impossible. We will now describe a method by which the disk of 

 Cassiopea when deprived of marginal sense-organs may be made to 

 pulsate indefinitely in sea-water with the production of effects no more 

 injurious than those of fatigue. This may be most readily accom- 



Fig. 7. Oral view of Cassio- 

 pea xamachana. Four of 

 the mouth-arms are cut off, 

 and the muscle layer of the 

 sub- umbrella in the upper 

 right-hand quadrant removed 

 to show the underlying vas- 

 cular system. ab, Mouth- 

 arm plate; ma, mouth-arm; 

 ml, muscular system of the 

 sub-umbrella; us, vascular ca- 

 nals of the sub- umbrella. 



plished by cutting off all marginal sense-organs, and then making a 

 series of concentric, discontinuous, ring-like cuts through the muscu- 

 lar tissue of the sub-umbrella, as is shown in figures 8 to 19.* Then 

 upon stimulating the disk in any manner it instantly springs into rapid 

 rhythmic pulsation, so regular and ceaseless as to remind one of the 

 movement of clockwork. The cuts must be so made as to permit 

 a free passage of contraction waves through sub-umbrella tissue form- 

 ing a closed circuit. The simplest circuit is, of course, a single ring 



* A glance at figure 7 will show that the muscular area of the sub-umbrella is a wide 

 annulus with the mouth-arm disk and stomach in the center. In figures 8 to 33 we 

 have represented the disk as a circle, the small concentric circle at the center being 

 the mouth-arm disk, while the wide annulus is the sub-umbrella. 



