June 21, 1924 
Morphology of the Honeybee Larva 
1199 
areas naturally diminish in size with the diminishing size of the trunk segments. 
The whole of this anterior half of the dorsal diaphragm is, however, so exceed¬ 
ingly delicate that it is difficult to determine accurately its structure in detail. 
In preparations showing the dorsal diaphragm in surface view, such as that 
from which Plate 7, A, was taken, in the segments anterior to the 5th abdominal 
segment the dorsal diaphragm appears as a cobweblike structure in which only 
the radiating muscle fibers can be clearly discerned. In sections the muscle 
fibers may occasionally be found, and here and there are indications of an ex¬ 
ceedingly fine structureless membrane; but the most conspicuous elements of 
the anterior half of the dorsal diaphragm are certain cells which may be called 
the anterior diaphragm cells. These are of relatively large size, and of pale 
appearance in stained preparations. The cytoplasm, besides being more trans¬ 
parent or less deeply stained, offers no peculiarities, and has a rather finely granu¬ 
lar appearance. The nuclei are elliptical and, unlike those of the posterior dia¬ 
phragm cells, are rather small as compared with the cytoplasm. In form these 
cells are irregular, although always flattened in a dorso-ventral direction. Their 
distribution is apparently scattered and irregular; some are found close to the 
heart wall, some at a considerable distance from it. Occasionally two or more 
are found associated together in small groups, attached end to end, but usually 
they occur singly. They never occur in long bands, as do the posterior dia¬ 
phragm cells. Although they are frequently found crowded in among fat cells, 
it is usually possible to discern a connection with either the diaphragm muscles 
or the diaphragm membrane, if not with the heart itself. 
The homology and function of these cells is unknown. On the basis of a 
study of the dorsal diaphragm, the writer (36), following Carriere and Burger 
(7), thought that but two kinds of cells, exclusive of muscle cells, were found in 
the dorsal diaphragm; small epithelial cells, forming the major portion of the 
diaphragm, and a smaller number of large cells, assumed to be homologous with 
the “paracardial” cells found by Heymons (14) in certain Orthoptera. The 
conditions found in older larvae, as described above, make this view untenable. 
Definite information regarding the function and homologies of the two kinds of 
diaphragm cells in the larva of the honeybee will undoubtedly demand extended 
inyestigation. 
VENTRAL DIAPHRAGM 
The ventral diaphragm is well developed in newly-hatched larvae (86) and in 
the imago (46) and forms a continuous sheet made up of transversely arranged 
muscle fibers overarching the ventral nerve cord and partitioning off a ventral 
(perineural) sinus. In older larvae it becomes merely a vestigial structure con¬ 
fined to the abdominal segments, and composed of more or less isolated delicate 
muscle fibers crossing the body cavity above the ventral nerve cord. They 
are entirely too few in number to form anything even approaching a membrane 
in structure, and constitute only a very loose and insignificant meshwork (PI. 
5, A, VDph). 
BLOOD 
The blood comprises a transparent fluid, the plasma, watery and only slightly 
viscid, and the blood cells (blood corpuscles, leucocytes) or amoebocytes. In 
the feeding larva the latter are of one sort only and correspond to the young 
amoebocytes of Cu6not (8). The amoebocytes of the bee larva are scattered 
throughout the spaces filled by the blood, but are usually more numerous in the 
dorsal sinus in the region of the heart. They vary in form from ovoid or ellip¬ 
soid to spherical, but the latter form is assumed only by cells preparing to divide. 
The ovoid form (fig. 5, C) is the one most frequently assumed by resting amoe¬ 
bocytes. In narrow spaces these are sometimes found slightly deformed by 
96463—24t-3 
