352 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
been described. Immediately on the division of the muscle into strands, 
the cells of these finer tracheoles begin very rapid mitotic division. 
Cells in various stages of division (cel. mit.) are to be found in nearly 
every section of a muscle in a stage similar to Figure 14 (Plate 6) and 
Figure 34 (Plate 7). Most of the new cells so formed become either 
actually or apparently detached from the tracheoles, and penetrate into 
the fissures between the muscle strands (cl. tr.). Some, however, re- 
main connected with the tracheae and show tracheoles, running through 
their cytoplasm (Figure 14, cl. tr.*). Especially in longitudinal sections 
(Figure 34, cl. tv.) they show long processes, which frequently connect 
with each other. These processes cause the cells to be of irregular forms, 
the spindle form being, however, the most frequent. The cytoplasm 
stains so deeply in thionin that the limits of the nuclei are in many 
cases difficult to determine. 
Fic. A. 
Other considerations than those mentioned above point to the origin 
of these cells from the cells of the walls of the tracheae. Figure A is 
a projection of the nuclei of the tracheal cells (represented by the small 
oval outlines) on an optical longitudinal section of the largest of the fibres 
of musculus metanoti (Plate 1, Figure 1, m#’nt.) to show the positions 
and numbers of these cells. The particular fibre chosen for this recon- 
struction was in an early stage of its metamorphosis, the reconstruction 
being made from a series of cross sections similar to Figure 14 (Plate 6). 
From the textfigure it is seen that near the places where the tracheae 
join the fibre, tracheal cells are much more numerous than elsewhere, 
and that they are distributed in just such positions as would be expected 
if they were being formed from the intracellular tracheoles which arise 
from the tracheae. This uneven distribution of the tracheal cells can 
scarcely be explained by assuming an origin of these cells from nuclei of 
the muscle fibre or from leucocytes. Mitosis is found in the cells of 
