EXPERIMENTS ON WORMS 91 



Harlier experiments had led me to suspect that the 

 "spontaneous" or "instinctive" burrowing was only 

 a reflex produced by the contact-stimuli of the sand. 

 I then attempted to find out whether it were not pos- 

 sible under special conditions to produce the same 

 reflex in brainless pieces. I placed such a piece of a 

 Nereis on the sand ; as usual it remained quiet. I 

 then gradually covered the forward end with sand. 

 The rest of the animal immediately began to make 

 the typical movements which the animal makes in 

 forcing its way into the sand. At the same time the 

 glands began to secrete the sticky substance which 

 cements the particles of sand together, forming the 

 wall of the burrow-hole. This secretion-phenomenon 

 regularly accompanies the burrowing of these animals ; 

 it is the same secretion that in other animals leads to 

 the formation of a case. 



But why does the Nereis not burrow when deprived 

 of its brain ? For the simple reason that it makes 

 use of the organs of the mouth in burrowing, and these 

 are amputated with the head. Hence it is the loss of 

 a peripheral head-organ which keeps the decapitated 

 Nereis from burrowing, and not the loss of the brain. 

 The brain in this case merely performs the function 

 of a segmental ganglion that is, it acts as the ganglion 

 of that segment to which the peripheral head-organ 

 belongs. 



5. We will now turn our attention to the brain- 

 functions of Nereis. 



After a Nereis has burrowed in the sand it lives in 



