348 MEDUSiE OF THE WORLD. 



This observation is, however, contrary to those of Yerkes and of Mayer, who noted irregular, 

 but spontaneous, pulsations of the center when in sea-water. Gonionemus, therefore, belongs 

 among those medusae (such as Aurelia and Dactylometra) which are not completely paralyzed 

 in sea-water by the removal of their central (marginal) nervous system. 



Loeb finds, however, that the center of the bell of Gonionemus beats very rapidly and 

 rhythmically in a solution of pure NaCl, and the more rapidly the higher, within certain 

 limits, the concentration of the NaCl solution. He also finds that the addition of small amounts 

 of CaCl 2 or MgCl 2 to the NaCl solution retards or inhibits the pulsations. Also any salt 

 which precipitates Ca or Mg, if added to sea-water, will cause pulsation in the center of 

 Gonionemus. Loeb therefore concludes that the center of Gonionemus is prevented from 

 pulsating in sea-water by the presence of Ca and Mg ions. 



Mayer, 1906, finds that the center of Gonionemus murbachu pulsates slowly, but con- 

 stantly and without pauses in a solution containing the amounts and proportions of NaCl + 

 KCI + CaCl 2 found in sea-water, but without magnesium. The pauses so characteristic of 

 the normal pulsation of Gonionemus are therefore due to the presence of magnesium in the 

 sea-water. It would seem, indeed, that pulsation is more powerfully inhibited by magnesium 

 than by calcium. 



In the case of Cassiopea, Mayer, 1908, finds that pulsation is so strongly stimulated in a 

 solution containing only the NaCl + KCl + CaCl 2 of sea-water that after many hours of vio- 

 lent contractions sustained tetanus, accompanied by a rupture of the muscles, is produced. 

 This tetanus may, however, be overcome and normal pulsation restored by adding to the solu- 

 tion of NaCl + KC1 + CaCl 2 the amount of magnesium found in sea-water. 



Magnesium, calcium, and potassium, through their inhibitory, or anesthetic, influence 

 overcome the too powerful stimulus due to Na upon Cassiopea. 



H. B. Bigelow, 1907, has carried out an elaborate study of the nuclear cycle in Gon- 

 ionemus murbachii. The somatic number of chromosomes is probably 24. No centrosome 

 is visible until the metaphase, and it is a minute granule at the focus of the spindle fibers, which 

 disappear after the anaphase. In the reconstruction of the nucleus the nucleolus is formed by 

 a condensation of chromatin granules. The egg aster disappears at the close of the second 

 maturation division. The spermatozoan enters the egg with its head and middle piece, but 

 the middle piece soon disappears. The sperm introduces the new aster, which centers at 

 some little distance from the sperm nucleus. This sperm aster then divides and forms two 

 asters which accompany the sperm nucleus in its migration through the egg. No sperm cen- 

 trosome was seen. Bigelow's paper abounds in important details and should be consulted 

 by those interested in the early developmental phases of the sperm or ova. 



Gonionemus agassizii Murbach and Shearer. 



Gonionemus agassizii, Murbach and Shearer, 1902, Annals and Mag. Nat. Hist., ser. 7, vol. 9, p. 73; Proc.Zool. Soc. London, 

 vol. 2, p. 185, plate 21, figs. 1-3; plate 22, fig. 3. — Kirkpatrick, 1903, Annals and Mag. Nat. Hist., ser. 7, vol. 12, p. 618, 



Bell about 20 mm. wide, 9 mm. high, hemispherical. 52 to 80 tentacles with thick bases 

 and well-marked peronial grooves. Tentacles about two-thirds as long as bell-diameter. 

 The lithocysts outnumber the tentacles in the ratio of about 3 to 2. Usually there are 2 litho- 

 cysts between each successive pair of tentacles, but they are quite irregular in arrangement. 

 Gonad much folded, color brown. Found in a small salt lake at Unalaska, Aleutian Islands. 

 Kirkpatrick's medusa from Japan is certainly G. depressus. 



Gonionemus depressus Goto. 

 Gonionema depressum, Goto, 1903, Mark Anniversary Volume, article I, p. 12, plate 2, figs. 10-13; plate 3, figs. 21, 22. 



When mature the bell is somewhat flatter than a hemisphere, and is about 20 mm. wide 

 and 8 mm. high; but when small it is relatively higher, for in a specimen 4 mm. wide it is also 

 4 mm. high. Bell evenly rounded, its walls of only moderate thickness. When mature there 

 are about 59 to 64 tentacles, which arise from the sides of the bell at a zone slightly above the 

 bell-margin. The entodermal cores of these tentacles traverse the gelatinous wall of the bell, 

 and are continuous with the entoderm of the ring-canal. All of these tentacles arise at one 

 and the same level. They are about as long as the bell-radius, are highly flexible, but not 



