A. D. Imms 
113 
(Figs. 9 and 15) 1 . In a transverse section only two of the cells are 
visible at any given place: they are crescentic in form and are united 
with each other along the dorsal and ventral lines. 
The lateral inlets or ostia are situated in pairs opposite one another 
on either side of the heart (Fig. 10). Each ostium is formed by a pair 
of enlarged cells which surround the aperture and are noticeable in 
stained preparations by their nuclei. 
The alary muscles ( al.vi. in Figs. 9 and 10) are markedly cross- 
striated : each muscle takes its origin from the integument on either 
side and, as it approaches the heart, it spreads out fanwise and divides 
and sub-divides so as to form a network of fine fibrillae. These fibrillae 
are arranged in the form of a dorsal and ventral sheet (Fig. 9), and in 
the space or interval left between them are situated the pericardial cells. 
In addition to the alary muscles, the heart is maintained in position by 
means of delicate strands of connective tissue placed at different 
points. 
The pericardial cells (Figs. 9 and 10) are placed laterally in relation 
to the heart, and form a chain of cells arranged in a linear series on 
either side. The cells are disposed with their long axes parallel with 
the length of the body, but the chains are not continuous throughout 
their leugth, numerous gaps or breaks in the series being present. 
They extend right through the abdomen to about the middle of the 
eighth segment. The cells contain several nuclei and their protoplasm 
is much vacuolated. In Sayomyia the pericardial cells were described 
by Wagner (1835) as “piriform bodies” and later by Dogiel as “apolar 
nerve cells” (1877, p, 9). In the anterior part of the thorax, and 
situated close to the heart on either side, is a longitudinal cord of 
multinucleated cells (Fig. 15). These two cords occupy very much the 
same position as the pericardial cells in the region of the abdomen and 
very possibly they are structures of a similar nature. 
The aorta is a forward prolongation of the heart through the 
thorax into the head. It has stout walls, and the nuclei of the cells are 
disposed with long axes parallel with the length of the tube. No alary 
muscles are present. The aorta passes forwards between the two 
dorsally placed cardiac coeca, and lies just over the oesophagus but, as 
it approaches the occipital foramen, it comes to lie nearer the dorsal 
integument. Just behind the brain, it becomes supported by an 
irregular mass of cells which envelops it both ventrally and laterally. 
1 In the larva of Sayomyia the nuclei project a long way inwards and were termed the 
“ stalked cells” by Leydig. 
