146 JULIA WORTHINGTON. 
ventrad as far as the base of the habenular ganglia. Ventral 
to this they are united. There are no superficial divisions 
of the lobes of the fore brain as there are of the olfactory 
lobes. 
On examining sections of the fore brain with the micro- 
scope the lobes are seen to consist of two parts, an outer 
shell, which is, however, from one to two thirds the thickness 
of the lobe, and extends over all but the ventro-caudal part, 
and asmall inner core (fig. 8). ‘The cells are of the same two 
kinds occurring in the olfactory lobes, but they are very 
differently arranged in the two parts. Those of the core are 
scattered through it without definite order. ‘The shell, on the 
contrary, shows a very marked arrangement of parts (fig. 8). 
First of all comes an outer layer, about ‘22 mm. thick, com- 
posed, probably, mainly of glia fibres and the dendrites of 
cells, and having cells scattered sparsely through it. Next 
comes the main cell layer, about the same thickness, for the 
most part, as the outer layer, and consisting of cells, crowded 
close together, with their long axes radially arranged. 
Inside of this is a third layer, similar to the first, and about 
the same thickness, only probably without so many glia 
fibres, and within this a thinner secondary cell layer, similar 
to the primary one. ‘The space between the secondary cell 
layer and the core is largely filled with fibre tracts. Of 
these, the most conspicuous one leaves the dorsal part of the 
primary cell layer, and runs caudo-ventrad, laterad of the 
core. As it nears the ventral surface it turns mesad, crossing 
to the other side in the post-optic decussation, and distributes 
itself in the floor of the ’tween brain. 
In the adult the lobes of the fore brain are solid, the 
ventricles having been obliterated by the encroachment of 
their walls on the ventricular cavities. In an embryo some 
little time before hatching the ventricles are very large, lying 
within the core, which is here much larger in proportion to 
the rest of the fore brain than in the adult. In this stage 
the shell lies cephalad and laterad of the core, but not dorsal 
to it, the dorsal wall over the ventricle being very thin. It 
