82 THE APODID^E PARTI 



belonged especially to the prostomium, taking the 

 antennal ganglia along with them on the com- 

 missures which continue to unite the brain with the 

 ventral cord. 



The transformation of the anterior pair of eyes 

 into the unpaired " eye " with other sensory functions 

 would bring about secondary complications. 



The gradual wandering of the ganglia of the first 

 antennae along the cesophageal commissures, or, if 

 these were already near the brain, their final union 

 with the same, added further complications. 



Lastly, when the antennae, and especially the 

 anterior pair, adopted a frontal position on the head, 

 and became important sensory limbs carrying 

 olfactory, auditory (? directive), as well as tactile 

 sensory organs, so that their ganglia became large 

 complex sensory centres at the posterior end of the 

 brain, its complication was completed, and it 

 reached the stage found in the higher Crustacea 

 (e.g.) Decapoda). 



At first sight, this method of deducing the Crusta- 

 cean nervous system from that of a bent Annelid 

 may not appear to the reader altogether satisfactory. 

 We may therefore perhaps anticipate what we shall 

 describe in its right place, and mention that when we 

 drew Fig. 18, to show where the brain was originally 

 placed in the more Annelidan ancestors of Apus, we 

 had quite forgotten that this was still the place which 

 it occupies in Limulus. In Part II. we hope to be 

 able to show that, if Apus is derivable from a bent 

 Annelid, Limulus must also have had the same 



