454 E inter on Growth and Inheritance 



are more like those of certain worms than they are Uke the 

 auditory organs of some other jelly-fishes; and, similarly, 

 the auditory organs of certain worms are more like those of 

 certain jelly-fishes than they are like the auditory organs of 

 some other worms. To the wonderful resemblance which 

 exists between the eyes of cuttle-fishes and time fishes it has 

 been objected that the disposition of the retina in the one is 

 the opposite to the disposition of the retina in the other, but 

 we have learnt from Semper that in the slug Onchidium the 

 retina, in these respects, agrees with that which exists in the 

 eyes of fishes and other backboned animals — including, of 

 course, ourselves. 



The truth that similar structures have thus arisen inde- 

 pendently tells with great force, as Professor Eimer says,^ 



* against the prevailing fashion of dogmatically referring all 

 similarities of form to blood-relationship.' 



Experiments performed by him on jelly fishes - lead him 

 to the conclusion — 



* that a single will can exist with a number of brains. ... I have 

 shown how the eight brains of Aurelia produce single movements ; the 

 impulse proceeds always from one of the brains, and passes immedi- 

 ately to the others — sometimes one, sometimes another originating the 

 impulse — ^but this does not exclude the possibility of all eight acting 

 at the same time ; indeed, this is probably necessary for the produc- 

 tion of certain movements.' 



He adds as a conclusion (which may startle some readers) 

 the assertion : — 



* Whether in a given animal there are eight such central points of 

 nervous activity or thousands — as many as there are nerve cells or 

 ectoderm cells on the body surface — makes no difference.' 



This assertion we have no more desire to contest than to 

 support. We regard it as an interesting speculation, but not 



1 P. 339. - P. 348. 



