74 THE APODID^l PART i 



commissures travelled upwards, describing part of a 

 circle, carrying up with them the two pairs of antennal 

 nerves, the pair of nerves which originally had the 

 more ventral position would naturally come to occupy 

 the more dorsal position, as shown in the diagram, 

 Fig. 19. 



If now we assume, as shown in the diagram, Fig. 20 

 that in the original Crustacean-Annelid the ganglia 

 of the first antennae had already travelled up the 

 cesophageal commissures to near the brain, then we 

 have to suppose that these ganglia split away with 

 the brain-cesophageal commissures, although, by 

 so moving off with the brain, they were dragged 

 further from the limb their fibres had to innervate. 

 This latter assumption, as shown in Fig. 20, agrees 

 best with the description of the central nervous system 

 given by Pelseneer. He assumes that a group of 

 ganglion cells, in the position marked x in Fig. 20, 

 form the ganglia for the first antennae, and he supports 

 this claim by the fact that the nerves branch back- 

 wards, as shown in Figs. 20 and 21. 1 If this reason- 

 ing is correct, then we may assume either (i) that the 

 migration of the ganglia had already taken place in 



1 Quarterly Joiirnal of Micro. Sc., vol. xxv. Although inclined 

 to believe Pelseneer's view to be correct, his arguments do not 

 seem to us quite conclusive. The results of our own research 

 unfortunately remained neutral. We should much like the point re- 

 examined ; perhaps the new method of staining the nervous system of 

 living animals with methyline blue would reveal the actual courses of 

 the fibres. In our own best hrematoxylin preparations the fibres 

 became suddenly quite confused where the antennal nerve joined the 

 commissure, and we could not say whether they ran on to the brain, or 

 bent back towards the infra-cesophageal ganglion. 



