1200 
Journal of Agricultural Research 
Vol. XXVIII, No 12 
pressure from the adjoining tissues, but no evidence of a true amoeboid move¬ 
ment was observed. Unlike the cells of many other organs and tissues of the 
larva, such as those of the mid-intestine and of the fat body, the size of the amoe- 
bocytes remains nearly constant throughout the life of the larva, and is from 6 
to 9 microns wide and 7 to 12 microns long. The cytoplasm stains moderately 
with the usual chromatin stains and normally presents no evident differentia¬ 
tions or inclusions. The nucleus is relatively very large, is spherical in form,, 
and contains a few small chromatin granules. Cells in mitosis are quite frequent 
(fig. 5, D-H) and it is easy to find a series representing the different phases.. 
This seems to be the normal if not the only mode of increase, since there is no 
good evidence of a special blood-forming tissue in the bee larva. 
Anglas ( 1 ) describes a second type of blood cell “lymphocyte,” larger, and 
with the cytoplasm finely vacuolated. This type apparently does; not appear 
in the larva prior to capping. 
The action of the heart and the flow of the blood are very similar to those of 
the imago, as described by Snodgrass (46 ), except that the sole propulsive organ* 
is the heart. Except in very young larvae, the ventral diaphragm is so poorly 
developed that its action must be practically negligible. In a mature living 
larva, removed from the cell, successive waves of contraction are seen to pass 
cephalad over the heart at the rate of about one per second at room temperature^ 
driving the blood into the head cavity. From here the blood flows caudad r 
filtering back through the channels formed by the various spaces between the* 
fat body and the viscera. Some of these spaces are sufficiently well defined to- 
deserve to be called blood sinuses. The most conspicuous of these is the ventral 
sinus (PI. 5, A, US), & tubular space extending the entire length of the larva 
above the ventral nerve cord and bounded laterally and dorsally by lobes of the* 
fat body. As the figure shows, it is not limited dorsally by the ventral diaphragm 
(VDph), as it is in other insects. Another considerable space is found between 
the heart and the alimentary canal, while a continuous space exists around the* 
mid-intestine, permitting a free flow of blood over the external face of the latter.. 
Around the tracheal trunks and their principal branches are also narrow spaces 
free from fat cells, which form blood channels. The pericardial chamber is more- 
or less completely filled with fat cells (the pericardial fat cells) except in the middle* 
of each segment, where there is a space on each side of the heart, opposite the 
ostia, which is unoccupied by fat cells. These spaces extend laterad from the 
heart a short distance, and each receives one of the dorsal tracheal branches 
(fig. 2, A), being thus connected with the blood channel accompanying this, 
branch. In the living larva blood may be seen flowing dorsad along this path. 
The pericardial blood lacuna just described may be seen in Plate 7 r A, in which 
the round pericardial cells are represented in dotted outline. It should be stated,, 
however, that these cells actually extend farther laterad than is shown, many 
of them having been removed in dissection. In the living larvae, and even iu 
some fixed specimens, these pericardial lacunae are evident externally as short 
dark bands extending right and left from the heart in.each segment (see PI. 1, E). 
FAT CELLS, OENOCYTES, EXCRETORY CELLS 
FAT CELLS 
At all stages except the earliest, fat cells, constituting collectively the so-called 
fat body, occupy approximately a half of the body cavity not already occupied 
b}^ the other viscera. In life the fat cells are nearly opaque and colorless. Since 
they underlie the transparent hypodermis over the greater portion of the body 
they are largely responsible for the ivory-white tint of the larva. In general, 
the fat cells adhere together in flat lobular masses or strings, supported by tracheae 
