190 SUMMARY OF CURRENT RESEARCHES RELATING TO 



its life. There was no evidence of correspondence between the be- 

 haviour of the sea-anemone and the tides. There is often alternation 

 of rest and activity, bnt without any regularity. 



Opening and Closing of Sea-Anemones.* — H. Pieron finds that 

 Actinia equina closes up when there is a diminution of oxygen in the 

 medium. It closes when the tide goes out as an adaptation to a medium 

 with a variable and often low supply of oxygen. The closing increases 

 its power of resisting asphyxia. 



Developmental Cycles of a Scyphistoma.t — E. Herouard describes 

 a Scyphistoma in the aquarium at Roscoff, which he has called Teeniol- 

 hydra, though it is apparently a peculiar phase of some known genus. 

 For four years it has formed cysts, each containing a blastula, which 

 develops into a polypoid embryo with two tentacles. No ephyrae were 

 formed in four years, but when Herouard fed the Scyphistoma with 

 sea-urchin ovary they budded off ephyrse. During the four years 

 without ephyras the animal had insufficient food, and simply budded 

 off polypoid stages like itself, or formed statoblasts with blastulaa as 

 already noted. 



Pulsation in Medusae. $ — A. G-. Mayer has studied the rhythmical 

 pulsations of Cas,siopea xamachana. Sea-water is a balanced fluid, 

 neither inhibiting nor stimulating pulsation. This is due to the fact 

 that the sodium chloride of the sea-water is a powerful nervous and 

 muscular stimulant, but the magnesium, calcium and potassium are 

 inhibitors. The sea-water itself being indifferent, permits any weak, 

 constantly present, internal stimulus, to produce the nervous responses 

 which cause rhythmical pulsation of the muscles. 



The stimulus which causes pulsation, is due to the constant forma- 

 tion of sodium oxalate in the terminal endodermal cells of the marginal 

 sense-organs. This sodium oxalate precipitates calcium, as calcium 

 oxalate, thus setting free sodium chloride and sulphate, which act as 

 nervous stimulants. Pulsation is thus caused by the constant main- 

 tenance at the nervous centres in the sense-organs of a slight excess of 

 sodium over and above that found in the surrounding sea-water. 



If we cut a strip of heart tissue, or of subumbrella tissue of a 

 medusii in such a manner as to give it the shape of a ring or of any 

 closed circuit, and then start a contraction -wave moving in any one 

 direction through this circuit, the wave will continue to travel at a 

 uniform rate around the circuit. This wave will maintain itself in- 

 definitely, provided the circuit be long enough to permit each and 

 every point in the path of the wave to remain at rest for a certain 

 period of time before the return of the wave through the circuit. No 

 one localised point on the circuit acts as a dominant centre for main- 

 taining the wave, but all points on the path of the wave take an equal 

 share in passing the wave onward to points beyond them. In nature 

 the structure of pulsating organs, and their manner of stimulation, are 



* Comptes Rendus, cxlvii. (1908) pp. 1407-10. 



t Op. cit., cxlviii. (1909) pp. 320-3 (lfig.). 



X Publications, Carnegie Inst. Washington, No. 102 (1908) pp. 113-31 (13 figs.). 



