620 



MEDUS.l!; OF THK WORLD. 



lathc-r than those of their normal parents, aiul thus the race as a whole maintains itself 

 unchanged. About 22 per cent of the ephyrae ami ot ailult .lurcllia have either more or less 

 than 8 marginal sense-organs. 



Most interesting ph\siological studies have been carried out upon Aurcllta by Romanes, 

 1885 (International Scientific Series, vol. 49, etc.\ and also hv Eimcr, 1878. These studies 

 show that the marginal sense-organs of AurAlui are locomotor centers which control the 

 rhythmical pulsation. These marginal sense-organs tend to send out impulses to pulsation 

 at various rates, but the fastest working sense-organ controls all the others and forces them 

 to beat at its own rate. Parts of the subumhrelia deprived of marginal sense-organs will still 



