70 THE APODID^E PART i 



above stated, come almost direct from the brain. The 

 other changes, brought about by the bending of the 

 segments, would be the disappearance of the longi- 

 tudinal commissures between the four or five fused 

 ganglia, and perhaps a fusion of at least some of their 

 transverse commissures. We shall see in the second 

 part of this book, when we come to compare Limulus 

 and Apus, that the nervous system of the former, 

 though showing certain special modifications of its 

 own, corresponds, to a remarkable degree, with that 

 of such a bent Annelid, and thus shows even a more 

 primitive state than that of Apus. 



Now let us consider the modification such a central 

 nervous system would undergo owing to the gradual 

 migration of the eyes on to the dorsal surface. Figs. 

 19 and 20 are two diagrams to illustrate the change ; 

 Fig. 19 supposing the ganglion for the first antenna to 

 come from the infra-cesophageal ganglion, Fig. 20 sup- 

 posing this ganglion to have already migrated along 

 the commissures to near the brain. The brain, follow- 

 ing the eyes, would divide the original cesophageal 

 commissures (ce^) longitudinally, thus producing two 

 cesophageal commissures, one (<2? 2 ) in its original 

 position, innervating the oesophagus and "the upper lip, 

 and the other (^ 3 ) carrying the brain and the eyes. 



This origin of the two cesophageal commissures in 

 Apus is especially interesting because it explains the 

 origin of the sympathetic nervous system in the Crustacea. 

 Reserving, however, this point for the present, we 

 have to consider the more difficult problem relating to 

 the position of the antennal nerves, and how they 



