198 THE APODID^ PART 11 



in Limiilus as homologous with the points of attach- 

 ment of the dorso-ventral muscles in Apus, marked 

 p in figures 66 and 6j. 



The Nervous System. — The nervous system of 

 Limulus is especially important and interesting. In 

 many respects it is more primitive than that of 

 Apus, for example, in the position of the brain. On 

 the other hand, again, owing to the greater special- 

 isation of the whole body, it is in some respects 

 more specialised. 



In describing our bent Annelid we naturally found 

 it necessary to assume that the brain was originally 

 in the prostomium or labrum. In Apus, owing to 

 the wandering of the eyes forwards and upwards, the 

 brain followed the eyes, splitting the oesophageal com- 

 missures into a sympathetic ring and a cerebro-oeso- 

 phageal ring. In Limulus the brain has retained its 

 original Annelidan position. It need hardly be said 

 that this is a very striking confirmation of our deriva- 

 tion of Apus from a bent Annelid. We had quite lost 

 sight of this fact when we stated that in the original 

 Crustacean-Annelid (shown in Fig. 18, p. 69) the 

 brain was in the prostomium, and that in Apus it had 

 wandered from its place through secondary adapta- 

 tions. Thus the very difference in the position of the 

 brains of Apus and of Limulus affords a conclusive 

 proof of their real relationship as derived from the 

 same bent Annelid. 



It is almost equally Important for our argument to 

 note that, as Ray Lankestcr pointed out, the brains of 

 Apus and Limulus are alike In constitution, both 



