No. 2:| MICRODEUTOPUS GRYLLOTALPA COSTA. 327 
same way that Bobretzsky ('74) describes for Oniscus. These 
become the liver tubes. Fig. 51 represents a section of an 
egg which is in about the stage shown in Fig. 38. The section 
passes somewhat obliquely through the region marked a-a. 
In the region of the dorsal organ the cells are arranging them- 
selves to form a tube on the left side of the body. The sections 
(Figs. 57, 58) of a stage between Figs. 38 and 42 pass through 
the lines a—a and 6-3, represented in Fig. 42. In the sec- 
tion lying nearest the dorsal organ (Fig. 58), where the greater 
mass of invaginated cells was found, the tubes are almost com- 
plete, and a mass of cells is still seen in the center of the egg. 
Only the dorsal walls are formed in the section nearer the 
anterior end, although in this case there are as many cells found 
in the part of a tube as there are in the whole tube of section 
(Fig. 58). This, however, is not always the case. The tubes 
are always complete in the region of the dorsal organ before 
they are complete in any other region of the body. Although 
no cell walls could be seen, the entoderm cells can be dis- 
tinguished readily from those of the ectoderm and mesoderm 
by their nucleiy and in one egg there was a little yolk space 
between the cells of the body wall and the liver tubes. In 
other eggs the tubes have been seen in various stages of for- 
mation; for instance, in one section, where there was a break 
in the wall of the tube, like the one shown on the right-hand 
side of Fig. 58, three cells were lying in the gap, but they had 
not sent out protoplasmic prolongations at the time to complete 
the tube. Ina section of an egg somewhat older (Pl. XXVII, 
Fig. 45), the liver tubes are complete in the region of the 
dorsal organ, and a few cells are found in the center of the 
yolk mass. Only in one instance have I seen an entoderm cell 
dividing. It was in the ring of the liver tube, and the plane 
of cleavage was parallel to the radius of the tube. I feel con- 
fident, however, that the cells must increase in number by 
division, because, as I shall show, most of the digestive tract 
is formed from entoderm cells. 
By this time the elongation and consequent folding of the 
embryo, described above, has been completed. The area 
between the dorsal organ and the last appendage now extends 
