78 THE APODID^E PART i 



other ventral ganglia in Apus have two transverse 

 commissures, that the transverse commissures of the 

 antennal ganglia were also originally double. On this 

 supposition, passing from the original Crustacean- 

 Annelid to the higher Crustacea, we should have two 

 separate fusions. First, in Apus, there is a fusion of 

 the double transverse commissures of the two pairs 

 of antennal ganglia, leaving two transverse com- 

 missures, one for each pair of antennal ganglia ; 

 then, in the higher Crustacea, these two single 

 transverse commissures of the two pair of ganglia 

 again fuse, so that there is only one transverse com- 

 missure joining the cesophageal commissure in front of 

 the infra-cesophageal ganglion. This transverse com- 

 missure, which is always assumed to be that of the 

 ganglia of the second antennae, would be, according to 

 this view, the fused transverse commissures of the 

 ganglia of both pairs of antennae, though the ganglia 

 themselves have wandered towards the brain. 



We can see no inherent difficulty in thus deducing 

 the central nervous system of Apus from that of a 

 bent Annelid ; none of the assumed transformations 

 are in themselves improbable, if the migration of the 

 eyes is once admitted. We shall return more than 

 once to this subject of the migration of the eyes, 

 especially in connection with the Nauplius and 

 Limulus, in each case bringing forward fresh evidence 

 in support of the assumption. In the meantime it 

 seems to us that the central nervous system of 

 Apus, taken as a whole, bears incontestable witness 



