ORGANIZATION AND GROWTH 221 



associated with this contraction stimulates the neighboring 

 nerves or muscles, thus causing the latter to contract. In 

 this way a conduction of stimuli is brought about without the 

 presence of a central nervous system, the effect of which is 

 the same as when a central nervous system is present. There 

 is so little difference between the latent period of stimulation 

 and the time the body remains contracted after the stimula- 

 tion, in the normal and in the brainless animal, that it can- 

 not be determined by mere observation unaided by special 

 apparatus. 



What occurs here in the entire animal happens in a lim- 

 ited portion of an earthworm when it is cut across trans- 

 versely and the two pieces are sewed together. As Benedikt 

 Friedlander has shown, both pieces are still able to perform 

 co-ordinated movements of locomotion. 1 I have repeated 

 the experiments of Friedlander upon leeches, and have 

 observed the same series of phenomena in them. 



Two years ago I made some observations upon a marine 

 Pianarian, Thysanozoon brocchii, which are similar in cer- 

 tain respects to those upon Ciona, into a discussion of which, 

 however, I cannot enter here. 2 



4. Since I had received the impression that Ciona is helio- 

 tropic, I tried to see whether a Ciona robbed of its nervous 

 system would also react to light by heliotropic bendings. 

 The object of my experiments was thwarted by an unwished 

 for, but perhaps interesting, result. In the course of four 

 weeks all the animals (which had not died) had regenerated 

 a new brain. I repeated the experiment, because I did 

 not believe my first results. But I can no longer doubt 



1 BENEDIKT FRIEDLANDER, Biologisches Centralbl., Vol. VIII (1889). 



2 The Darwinians would probably call the reaction of a Ciona intestinalis to 

 contact the consequence of a "protective instinct." These "protective instincts," 

 so far as I can see, are said to consist in this, that the animal has by natural selec- 

 tion acquired, in the course of the customary million years, certain cerebral con- 

 trivances which are now inherited from one generation to another. But in the case 

 of Ciona these hereditary " instincts " cannot well be located in any special portion 

 of the brain, for they continue to exist after the removal of this organ. 



