THOMPSON: METAMORPHOSES OF HERMIT CRAB. 
179 
numerous in the glaucothoe, the cell groups still are indistinguishable 
and confluent. But by the time the adolescent stages are reached 
the groups though still united, become identifiable. The median 
ventral group, the cellulae mediates, is the first to become com¬ 
pletely distinct and separate, in crabs forty days past the glaucothoe. 
The adult separation of all groups was found in the Wareham crabs. 
The globuli of the brain decrease in size in the earlier stages more 
rapidly than do the fiber masses. The diameter of each bears the 
following ratio to the width of the latter, measured in coronal or 
transverse sections at different periods : — 
Stage 
Diameter of Width of 
globulus. intervening liber mass. 
Adult 
Sixth stage 
Fifth stage 
Second stage 
First stage 
1 
1 
1 
1 
1 
1.42 + 
2 
2 
2.6 
3 
The infra-oesophageal ganglion has a history similar to that of 
the supra-oesophageal. The zoeae have small fiber masses which 
are deeply imbedded in ganglion cells and these latter are especially 
prominent on the ventral side of the ganglion. In surface view, 
therefore, the ganglia would exhibit as great a degree of concen¬ 
tration as in the adult, but in reality the individual fiber masses are 
much more distinct, especially those for the maxillijjedal and max¬ 
illa segments. The fiber masses for the limb segments are very 
small in the zoea phase. With the glaucothoe, the cheliped gang¬ 
lion alone shows a ventralward projection, this detail appearing for 
the other limbs in the adolescent phase. Nerves pass to the rudi¬ 
mentary limbs in the fourth zoea. 
The three earlier zoea stages have possible traces of the first 
abdominal ganglion in two minute fiber masses that lie outside 
of the thoraco-abdominal commissures at their origin. Nothing of 
this can be detected later. The length of the segments of the 
abdomen is more nearly equal during the zoea and glaucothoe 
phases than during later life, and hence the five abdominal ganglia 
are nearly equidistant from one another at these periods. Both 
ganglionic and commissural nerves are present from the first zoea 
(pi. 7, fig. 29). At the close of the glaucothoe period, after the 
