Turner, Mushroom Bodies of the Crayfish. 345 
Latero-ventral Nidus (fig. 1, 5, L.V.N.). This is a small 
cluster of cells which occurs on the caudal aspect of the latero- 
ventral portion of the brain. It covers the caudal portion of the 
antennary nerve. The cells of this cluster resemble those of 
the dorsal nidus. 
Ventral Nedus” (ties, 1.2; : 17, VoL.) . This ‘ts“'a~ ¢lus- 
ter of cells occupying the cephalic portion of the ventral side 
of the brain. Histologically it resembles the dorsal and latero- 
ventral nidi. On the cephalic aspect of the brain the dorsal 
and ventral nidi practically more or less unite, by means of 
neuroglia cells. 
LoBES OF FIBRILLAR SUBSTANCE. 
The histological groundwork of the Decapod brain is com- 
posed of a meshwork of fine fibrils which has been variously 
called ‘‘Punktsubstanz’ (Leypie), ‘‘Marksubstanz’’ (DIETL), 
‘fibrillar substance’ (Kenyon), etc. This fibrillar meshwork is 
segregated into more or less distinct fibrillar structures. In this 
paper these separate clusters of fibrillar substance are called 
lobes. 
This paper recognizes eight paired and two unpaired lobes 
which are of sufficient importance to deserve mention. Six of 
these paired lobes and the two unpaired lobes are situated in 
the median portion of the brain; while the remaining two 
paired lobes are located in the lateral swellings. In the median 
portion are found the following lobes: dorsal lobe, inferior 
dorsal lobe, antennulary lobe, tegumentary lobe, antennary 
lobe, pyriform lobe, the procerebral bridge and the central 
body. In the lateral swellings are found the optic and olfac- 
tory lobes. Even when all of these lobes have been located it 
will be seen that there is still a portion of the fibrillar substance 
left in which these various lobes are imbedded, 
Most of these lobes have been described and located by 
Krikcer (88). The following table will show how the lobes 
here described correspond to those described by him. 
