1178 
Journal of Agricultural Research 
Vol. XXVIII, No. 12 
appearance, while the nuclei frequently stain very intensely with iron haema- 
toxylin (PI. 3, C, Nlm ). An inner neurilemma is present as a more or less regular 
layer of small cells lying between the ganglion cells and the fibrous substance. 
It is best developed and most early seen in the brain (PL 2, B, I Nlm), and less 
so in the smaller ganglia. (PI. 3, C, I Nlm.) 
The brain and other parts of the central nervous system present in sections 
the usual core of nerve fibers and the cortical zone of nerve cells. (Pl. 2, A 
and B.) In the larval brain many of the features of the imaginal brain are 
plainly recognizable. This is particularly true of the broadly expanded optic 
lobes, which in transverse sections clearly display a division into inner, middle, 
and outer fibrillar masses (Pl. 2, A, fm3, fm2, fml ), while the cells and their 
fibrous processes show a distinct radial arrangement. In Plate 2, A, a layer of 
fibers intermingled with small cells is seen situated near the lateral faces of the 
optic lobes, between the latter and the hypodermis. These are evidently the 
developing postretinal fibers ( PrF ). They enter the optic lobes on the posterior 
surface of the latter, near their lateral margins, and may be traced around their 
lateral margins to the optic plates. The latter comprise two crescentic thick¬ 
ened areas of the hypodermis (ectoderm), one on each side of the head, their 
extent and relation to the remainder of the head capsule being indicated by 
Plate 2, C, OpPl. 
The ocelli are present at this stage as hypodermal thickenings. Those for 
the two lateral ocelli are shown in Plate 2, A, 0. The rudiment of the median 
ocellus lies farther cephalad, in the median groove (43). 
Centrad and somewhat cephalad of the optic lobes, the rounded protocerebral 
lobes (Pl. 1, B, IBr) are seen to contain well-developed mushroom bodies, which 
are essentially similar to thosoof the imago (Pl. 2,*B, MB). These bodies were 
found to be recognizable in a larva three days old. 5 
The deutocerebral or antennal lobes, although not evident externally, are 
distinguishable in sections by corresponding enlargements of the fibrous core 
(Pl. 2, A and B, AntL), and the relatively prominent tritocerebral lobes are 
similarly characterized (SBr). 
The internal structure of the ganglia of the ventral nerve cord of the bee 
larva is simple, offering no striking peculiarities, and may probably be con¬ 
sidered as fairly typical of the condition generally found in the simpler types 
of insect larvae. As seen in Plate 3, B, which represents a transverse section 
through the fifth abdominal ganglion, each ganglion is divided externally into 
right and left halves, representing the two members of the pair of primitive 
single ganglia. The outer surface of the ganglion is covered by a well-defined 
neurilemma (Nlm). Internally each lateral half consists of a central mass of 
nerve fibers, continuous with that of the connectives and surrounded by ganglion 
cells (NvF). These two central masses of nerve fibers are connected with one 
another by two parallel transverse strands of nerve fibers, the commissures 
(Pl. 3, B and C, Com ). These are, as shown in Plate 3, C, situated somewhat 
cephalad of the middle of the ganglion. On the left side, in Plate 3, B, a strand 
of fibers (LNvF) is seen passing laterad from the central mass of fibers. On 
the right side the ganglion is seen to extend itself laterally into the lateral nerve 
of this side, in which is seen a strand of fibers (LNvF) corresponding to 
that of the opposite side. On the right side, however, the connection of the 
nerve fibers of the lateral nerve with the central mass is not shown in this 
section. 
8 The duration of the feeding period of the larva is from four and one-half to five and one-half days. 
Larvae taken at or near the end of this period are considered mature, and it is to such larvae that the 
description above applies, unless otherwise stated. 
