362 WHEELER. [Vou. III. 
distance between the dorsal edges is greatly lessened. The 
transformation of the original ribbon of several superimposed 
rows of cells into the simple epithelium of columnar cells is not 
entirely due to cell division. As may be seen from Figs. 84 
and 85, either the wandering of the inner rows of cells over the 
outer towards the dorsal edge of the ribbon, or a stretching of 
the whole band, so as to permit an intercalation of the cells 
of the inner rows between those of the outer row, are the more 
probable factors in the thinning out of the entoderm. The 
latter method is more probable, though the former method is 
certainly in keeping with the gliding and mobile movements of 
the entoderm. The nuclei of the entoderm have their chromatin 
distributed in the typical filament, which is more attenuated 
than in either mesoderm or ectoderm nuclei. Shortly before 
hatching the chromatin of the mesenteron nuclei appears to 
have dissolved, as they seem to have become perfectly homo- 
geneous, though they still stain deeply. In the hatching larva 
the cells have become more deeply columnar, on account of a 
diminution in calibre of the mesenteron. The nuclei cease to 
absorb more of the staining fluid from the surrounding cyto- 
plasm, though the walls retain their evenly rounded contour. 
Such a fundamental change in the nuclei would seem to indicate 
that some important change is about to take place in the mes- 
enteric layer of cells; but whether this change is dissolution I 
am unable to say, as I have not studied the insect in the stages 
beyond hatching. 
The process of mesenteron formation is essentially the same 
in Blatta as that just described for Doryphora. From the first, 
the entoderm cells of 4/a¢ta are as small and indistinct as the 
yolk cells are large and prominent. They form, as stated above, 
two bands of very flat cells bearing the same relations to the 
mesoderm as the corresponding bands of Doryphora (Fig. 54 
ent). The edges of the two ribbons continue their growth, and 
meet ventrally and dorsally, to complete the mesenteron (Fig. 
55 ent). 
Besides the lining of the mesenteron the corpus adiposum, 
represented during the embryonic life of Doryphora by a number 
of granular cells which constantly increase in size up to the time 
of hatching, probably originates from the entoderm. I have 
observed in several cases that before the two posterior bands of 
