36 PUWATION OF JEL-LYFISHES. 



Dactylometra maintain these pulsations is only a little higher than that 

 maintained by its marginal sense-organs. For example, a Dactylo- 

 metra which pulsated 39 times per minute when intact pulsated 46 

 times per minute with perfect regularity when all sense-organs were 

 removed and partial rings were cut in its sub-umbrella. 



It will be recalled that Romanes briefly mentions a specimen of the 

 hydromedusa Staurophora laciniata, in which there were three centers 

 of spontaneous contractions after the bell margin was removed. I have 

 not succeeded in causing the disk of Gonionenius to pulsate contin- 

 uously by cutting partial rings in its sub-umbrella after the margin 

 had been removed. There were, however, but a few small specimens 

 at my disposal. As Yerkes found, the central disk of Gonionemus , 

 when deprived of its margin, often gives isolated contractions without 

 external stimulation. 



III. REACTIONS OF CASSIOPEA TO CHEMICAL STIMULI. 



CHBMICAL STIMUI,ATION OI? PARALYZED DISKS. 



As we have seen, the loss of the marginal sense-organs paralyzes 

 the disk of Cassiopea, but it still reacts strongly by contractions if the 

 surface of its sub -umbrella be touched by certain substances, while 

 others have no effect upon it. 



Strong solutions or crystals of the following produce contractions: 

 KAl(SOi)2, KBr, KCN, K2CO3, KCl, KCIO3, KjCrO,, KsCraO^, 

 KgFeaCiaNiaeHjO, KI, KMnO^, KNO3, KOH, KHSO,, K2SO,, 

 K2S2O7; also NajCOs, NaHCOg, NaCl, NaClOj, Na2HP04l2H20, 

 NaNOg, NaOH, NaS037H20, Na2SO4l0H2O, and sodium oxalate ; 

 also IviCl, BaCl22H20, BaSOi, Ba(OH)2, NH^OH, glycerin, dextrose, 

 CuSOi, Fe2Cl6, PtClj, and iodine, etc. Contractions are also produced 

 by very weak solutions of the following acids: Acetic, chromic, oxalic, 

 sulphuric, hydrochloric, picric, nitric, and formic. This effect is doubt- 

 less due to hydrogen, the only element common to all of these acids. 



The following substances produce no contractions, even when the 

 crystals themselves, or their saturated solutions, are applied to the 

 surface of the sub -umbrella : MgBr, MgCl2, MgCOa, MgSOi,- also 

 CaCOs, CaCl2, CaO, CaSOj, and SrCOg, SrClaGHjO, SrSO^, HgCl^, 

 FeSO^THjO, CH^NjO. 



Summarizing the above, we see that all salts of potassium, sodium, 

 lithium, barium, and platinum produce contractions, as do also weak 

 solutions of acids, glycerin, dextrose, ammonia, and iodine. By far 

 the strongest contractions are produced by potassium salts, while 

 sodium salts produce much weaker effects. Nevertheless the NaCl 

 of sea-water is a more powerful stimulant than the potassium (K2SO4 



