SECT. V THE NERVOUS SYSTEM 75 



the original Annelid^ and is inherited by Apus, or 

 (2) that the formation of the compound sensory 

 nervous centre (the syncerebrum of Lankester) has 

 taken place in Apus by the wandering of the first 

 pair of ganglia to join the brain. The former seems 

 to us the more natural conclusion, considering 

 the great difference in the distances between the 

 brain and antennae of an Annelid, and between 

 the same parts in Apus, We mean that the great 

 distance between the cerebral position of the ganglia 

 of the first antennae and the antennae themselves in 

 Apus, which seems unnatural, is best explained by 

 assuming that this cerebral position of the ganglia 

 was derived from the Annelid, where, owing to 

 the proximity of the antennae to the brain, it is 

 most natural. On the other hand we think the 

 second view the less probable, considering {a) the 

 weak development of the first antennae in Apus, and 

 (b) the distance of the eyes from the antennae, and the 

 difficulty of correlating their respective sensations, the 

 eyes pointing forwards and upwards, the antennae 

 backwards and downwards. 



In the higher Malacostraca, with well-developed 

 antennae placed close to the eyes and functioning as 

 auditory, olfactory, and tactile sensory organs, there 

 w^ould be no difficulty in imagining the migration of 

 the ganglia to have taken place in the course of their 

 development. But, as already stated, it is dif^cult to 

 imagine this in the case of Apus, and it is easier to 

 suppose that the fusion of the antennal ganglia with 

 the brain had already taken place in the original 



