_ 
TuRNER, Mushroom Bodies of the Crayfish. 331 
The tritocerebrum, which gives nerves to the second an- 
tenna, is composed of a pair of oesophageal ganglia, rigorously 
comparable to the oesophageal ganglia of the insects and of a 
pair of nervous masses, the antennary lobes, intercalated be- 
tween them. From the ventral surface arise the antennary 
nerve and from the dorsal the tegumentary nerve and the nerve 
to the eye stalk. The antennary lobes are united, not by com- 
missures, but by a band of ‘punktsubstance.’ 
Thus from the standpoint of brain structure the insects, 
myriopods and peripatus form a homologous group. 
The Brain of Limulus and Arachnids. The brain is com- 
posed of only two segments: the protocerebrum and the deuto- 
cerebrum. 
The protocerebrum is rigorously. similar to that of the in- 
sects. In Limulus the mushroom bodies are enormously 
developed. 
Among the crustacea, myriopods and insects, the deuto- 
cerebrum is pre-oesophageal and innervates the first antenne. 
In Limulus and Arachnids it is also pre-ocsophageal, but inner-_ 
vates the chelicera. There are no olfactory lobes and the trito- 
cerebrum is absent. 
In the following table VIALLANEs has summarized some of 
his conclusions. 
