366 KANSAS UNIVERSITY SCIENCE BULLETIN. 



XXXVII), and the other made up of larger cells as shown in 

 longitudinal section {f, fig. 3, and fig. 8). These cells often 

 contain a network of fibers, as seen in figure 8, and also 

 structures resembling nerve-cells (n) . 



In cross-section the heart-muscle appears to be striated, but 

 this is probably due to shrinking of the muscular structure, 

 thus causing the outer tissue-covering to arrange itself in 

 folds. 



On either side of the heart-tube is a tracheal tube (figs. 2 

 and 3, t), which makes connection with a spiracle in each 

 segment. 



Besides these structures, four distinct kinds of cells are to 

 be found between the alary muscles and the chitin : First, the 

 compact fibrous layer (b, fig. 2) next to the alary muscles. 

 Numerous fibers, muscle, and perhaps nerve, extend through- 

 out this layer. The cells are close together, and the nucleus 

 is quite large. 



The next and most numerous group of cells is the connective- 

 tissue, or pericardial, cells, which loosely fill the cavity between 

 the more compact ventral and dorsal groups. These cells are 

 shown at c, figures 2 and 3, and again at figure 5. Some in- 

 vestigators call them fat-cells, but I see no reason why they 

 should be called that. They are more or less fibrous, too, ir- 

 regular in shape, vary somewhat in size, and contain a rather 

 large nucleus with many spherical chromatin bodies. Two 

 nuclei are often to be seen in a single cell. 



Scattered throughout these cells are structures that very 

 much resemble nerve-cells (i, fig. 2), but they are probably 

 only another form of connective-tissue cells. 



The most dorsal layer of tissue contains two distinct kinds 

 of cells (fig. 2, d and e). Those again shown at figure 6 are 

 found in the greatest abundance. They are arranged in rows 

 (usually only one) along the dorsal wall next to the chitin. 



The cytoplasm in these cells forms a network throughout the 

 cell. The nucleus is large, with many deeply staining chro- 

 matin bodies. 



Scattered among these cells, at apparently no regular inter- 

 vals, are the cells, probably the same as Dogiel called ganglion- 

 cells. These cells are shown at e, figure 2, and again a single 

 cell enlarged at figure 4. 



These are the cells that are not shown with most of the 

 fixatives. The chrome-oxalic mixture and Nissl stain, or 10 



