322 C. F. MARSHALL. 



In all these cases the movements of the appendages in front of the 

 ganglion stimulated were slight: hence the normal passage of the 

 nervous impulse is down the cord : but if the cord was cut behind the 

 ganglion stimulated, the appendages in front of the ganglion moved 

 more strongly when the latter was stimulated than before. 



Summary of Results. 



1 . Motor and sensory roots analogous to those by which the spinal 



nerves of vertebrates arise do not exist in the lobster. 



2. There is no marked decussation of the nerve fibres in the central 



nervous system : but nervous impulses readily travel 

 across the ganglia from one side to the other. 



3. Each ganglion is a reflex centre for the appendages which it sup- 



plies. 



4. There is a distinct sense of touch which can be exercised through 



the thick cuticle of all parts, especially in the large claws. 



5. The cerebrum or supra-cesophageal ganglion is the seat of origin of 



inhibitory impulses : reflex actions are much more marked 

 when the connection between this ganglion and the rest 

 of the nervous system is severed. 



6. All the ganglia, including the cerebrum, are sensitive, i.e. respond 



to stimulation. 



7. The normal passage of the nervous impulse is down the cord, but 



when this path is interrupted, it will pass up the cord. 



It will be seen that the two most important results of these investi- 

 gations are negative ones. There is no marked decussation and there 

 are no separate motor and sensory roots. Nevertheless it is important 

 to have determined these points in such a highly organised inverte- 

 brate animal as the lobster. It would be interesting to investigate 

 these points in other highly organised invertebrates, such as the In- 

 secta, Arachnida, and Cephalopoda. 



