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SCIENCE 



[N. S. Vol. XXV. No. 645 



gous to that of unstable equilibrium, thus 

 allowing weak internal stimuli to produce 

 recurrent movement. 



In the lower marine animals the NaCl, 

 calcium and potassium of the sea-water 

 combine to form a powerful stimulant, 

 which if unchecked would produce only 

 sustained tetanus, but the magnesium over- 

 comes this effect by its anesthetic (dias- 

 tolic) influence. 



The pulsating organs of terrestrial ani- 

 mals are also stimulated by optimum com- 

 binations of NaCl, with potassium and cal- 

 cium, and this is held in check by a definite 

 proportion of magnesium. 



A Einger's solution resembles this opti- 

 mum combination of NaCl, calcium and 

 potassium, and is only a stimulant, not an 

 inorganic food. It must be counterbal- 

 anced by magnesium in order to enable it 

 to sustain pulsation indefinitely. 



In Cassiopea any paralyzed strip of sub- 

 lunbrella tissue, cut in the shape of a closed 

 circuit, will remain indefinitely in rhythm- 

 ical pulsation, if once a contraction wave 

 be started in the circuit. Every time this 

 wave returns through the circuit of tissue 

 to the place whence it started, it is re- 

 stimulated and sent forth anew, and being 

 thus reinforced at each return it is sus- 

 tained indefitnitely. 



In the seyphomedusa, Cassiopea, the dif- 

 fuse nervous or epithelial elements of the 

 sub-umbrella transmit the pulsation stim- 

 ulus to which the muscles respond by con- 

 traction. 



The peripheral muscular layer of the 

 wall of the loggerhead turtle's heart is the 

 only part actively concerned in the rhythm- 

 ical movement, and the internal cavem- 

 ated mass of the heart's tissue may be re- 

 moved without checking the pulsation. 

 This peripheral part of the muscular wall 

 of the heart tends to maintain itself in 

 pulsation very much as wiU circuits made 

 of the sub-umbrella tissue of Cassiopea. 



The pulsation-stimulus acts solely upon 

 the peripheral muscular layer of the heart's 

 wall, the inner cavernated tissue remaining 

 passive. 



The above is a brief review of Publica- 

 tion No. 47 of the Carnegie Institution of 

 Washington, ' Rhythmical Pulsation in Scy- 

 phomedusEe,' 1906. 



The Interrelation of Sensory Stimulations 



in Amphioxus: G. H. Parker, Harvard 



University. 



To weak acid solutions and other like 

 mixtures the anterior end of Amphioxus 

 was found to be most sensitive, the pos- 

 terior end less so, and the middle trunk 

 region least sensitive. To the pressure of 

 a camel 's hair brush, the middle region was 

 less sensitive than the two ends, which, 

 however, were not distinguishable one from 

 the other by this method of stimulation. 

 To a current of warm water (40° C.) the 

 anterior end was most sensitive, the middle 

 less, and the posterior end least. There 

 were no reactions to a current of cold water 

 (2° C). To a fine beam of strong sun- 

 light, previously passed through water to 

 eliminate heat, the anterior end including 

 the 'eye spot' was not sensitive, the region 

 immediately behind the 'eye spot' was most 

 sensitive, the posterior region slightly less 

 so and the middle region least so. 



The distribution of sensitiveness to light 

 corresponds to the distribution of the pig- 

 ment cups in the central nervous organ and 

 these cups are without doubt the mechan- 

 isms concerned with the reception of light. 

 The distributions of the other classes of 

 sensitiveness are in mutual agreement, and, 

 from the nature of their stimuli, these 

 classes are doubtless represented by integ- 

 mentary nerve terminals. To what extent 

 these classes are independent may be in- 

 ferred through the effects of exhaustion. 

 After the tail of Amphioxus has been re- 

 peatedly stimulated with weak acid, the 



