546 _ Prof. EK. A. Minchin. Report on the [Aug. 17, 
The hindermost chamber of the heart appears to end blindly posteriorly, 
A little way in front of the hinder end are attached the two large alary 
muscles, the largest of the whole series; not far in front of these again are 
the two ostia, on the sides of the widest part of the chamber. In front of 
the ostia the lumen of the heart narrows rapidly, and to the narrowed portion 
is attached the next pair of alary muscles, lying in the hinder part of 
segment IV. This arrangement is continued in segments II, III, and IV, the 
dilated portion of the chamber, with the ostia, occupying the middle of the 
segment, while the alary muscles, attached to the constrictions between the 
chambers, lie in the posterior regions of the segments. The alary muscles of 
these three segments are of moderate size. In segment II the heart receives 
a pair of tracheal tubes, right and left, which come to it opposite the ostia, 
and fork at once into branches running forwards and backwards. The alary 
muscles corresponding to the first abdominal segment are very small and 
difficult to make out, and the region of the heart to which they are attached 
does not show the slightest diminution or constriction of its lumen, as is the 
ease in all the chambers posterior to it. In front of the first pair of alary 
muscles, at the usual interval, are the two ostia, quite similar to those of the 
other chambers. In front of the first pair of ostia the lumen of the heart 
narrows to form a thin-walled vessel, which passes through the waist to 
become the artery which I have termed above the thoracic aorta. This last 
runs along the thoracic intestine on its dorsal side, and is continued over the 
stomach, remaining apparently quite independent of the digestive tract, and 
only loosely attached to it, until it reaches the cesophagus. Here it is firmly 
attached and becomes considerably dilated. A short distance in front of the 
stomach a conspicuous cushion-like mass of large cells lies over the aorta. 
At first I took this structure for a ganglion, but it appears to be a sort of 
lymphatic gland, judging from its appearance in sections, The thoracic aorta 
is apparently continued through the neck into the head, but I have not been 
able to follow its course further than the thorax. 
The microscopic examination of the heart shows further that its floor 
is composed chiefly of fusiform cells resembling unstriped muscle-fibres, 
while its sides are made up of gigantic cells with nuclei of corresponding 
proportions. These cells are arranged with perfect regularity, and in a 
manner exactly similar on the two sides of the heart, Hach ostium is 
formed by two cells, which are of small size when compared with the 
huge cells building up the wall of the heart, but are very large when 
compared with the cells of the surrounding tissues. Two of the giant 
cells intervene on each side between the hinder end of the heart and 
the fifth pair of alary muscles; two more between these muscles and 
