June 21,1924 
Morphology of the Honeybee Larva 
1207 
And of uniform diameter except at its anterior end, which is enlarged and closed 
Anteriorly by a thin diaphragm-like membrane which is closely applied to the 
extreme posterior end of the mid-intestine. The hind-intestine is clothed with 
a well-developed muscular coat composed of an inner layer of circular (trans¬ 
verse) muscle fibers and an outer layer of longitudinal fibers. Posteriorly the 
hind-intestine terminates in a slit-like anus. Here the hind-intestine is provided 
with muscle fibers which act as dilators. 
(8) The Malpighian tubules are long and winding, extending cephalad to the 
region of the metathorax. Their tapering and pointed posterior (central) ends 
are blind and are inserted between the posterior extremity of the mid-intestine 
and the thin epithelial layer closing the anterior end of the hind-intestine. In 
young larvae the Malpighian tubules are slender, with a small lumen and rela¬ 
tively thick walls; in old larvae they attain a relatively large diameter and pos¬ 
sess very thin walls, being obviously much distended. After the cell occupied by 
the larva has been sealed and communication between the mid- and hind-intestine 
has been established, permitting the discharge of feces, each of the Malpighian 
tubules acquires an opening into the mid-intestine by means of a minute canal 
perforating the annular remains of the epithelial layer which formerly closed the 
anterior end of the hind-intestine. The discharge of the fluid excreta of the 
Malpighian tubules thus occurs simultaneously with the discharge of solid 
excreta from the mid- and hind-intestines. 
(9) The silk glands comprise a pair of slender tubes, thrown into numerous 
short convolutions and extending nearly the entire length of the larva, below the 
mid-intestine. Their anterior ends unite to form a thin-walled duct, lined 
with chitin, which opens by a slit-like aperture on an elevation situated on the 
tip of the labium. 
(10) The trunk muscles are the same in all the abdominal segments except 
the 10th, and are (1) ventral longitudinal, a group occupying the sternal region 
of each segment and connecting its anterior and posterior margins; (2) ventral 
oblique, a pair of flat bands running obliquely cephalad and mesiad across the 
sternal region and also connecting the anterior and posterior margins of each 
segment; (3) lateral oblique, comprising one stout band crossing the lateral region 
of each segment in a cephalad and mesiad direction and connecting the two 
margins of the segment, and a small band crossing the lateral region in 
the opposite direction and having its dorsal end attached to the body wall in the 
region of the spiracle; (4) two small dorso-ventral bands; (5) dorsal longitudinal 
muscles connecting the anterior and posterior dorsal margins of the segments; 
(6) dorsal oblique muscles running from the posterior margin of each segment, in 
the dorso-lateral region, obliquely cephalad and mesiad to an oblique line of 
attachment on the body wall, the sutural line separating the prescutum and the 
scutoscutellum. Since the body wall is nowhere rigid, the arrangement of the 
muscles is responsible, to a large extent at least, for the external contour of the 
larva. 
*(11) The heart is a thin-walled tube, blind at its posterior end and running the 
entire length of the body in the mid-line close to the dorsal body wall, and con¬ 
tinuous cephalad as the aorta, which enters the head. The structure of the 
larval heart closely resembles that part of the imaginal heart lying in the abdomen. 
It posses a pair of valvular ostia in every segment except the 1st (possibly also 
the 2d) thoracic segment and the 9th and 10th abdominal segments. The heart 
is composed of two rows of flat cells on each side of the mid-line. The cytoplasm 
of these cells is differentiated to form striped muscle fibers. Externally the heart 
is clothed with a network of branching minute connective tissue cells. A dorsal 
diaphragm is present which is especially well-developed in the 4th to, the 9th 
abdominal segments, where it is composed largely of sinuous bands of small 
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