EMBRYOLOGY OF BDELLODRILUS ie 
2. MIDDLE STRATUM OF THE GERM BANDS 
The middle stratum of the germ bands can readily be dis- 
tinguished while the embryo is still nearly spherical. Upon 
close examination it is seen that the ectoblast cells are arranged 
into four distinct rows, on either side of the median ventral axis 
(figs. 65-66). Each row terminates posteriorly in a large cell 
or teloblast. 
Text figures 15 and 17 and figure 58 show the early formation 
of these rows of cells. Sections of these various stages show that 
Fig. 14 Surface view from upper pole, to show the position of the ten telo- 
blasts. The meso-teloblasts or mesoblasts have budded off eight or ten cells 
in the formation of the mesoblast bands. Their position is indicated by dotted 
outline. The broken outline represents the region of the entoderm. The 
position of the ectoderm is indicated by a continuous line. 
Fig. 15 Third horizontal section from the top, passing through four of the 
large nephroblasts. The spindles represent the beginning of the first division 
in the formation of the middle germ band. The anterior end and the right side 
of the section are a little below the horizontal plane. 
Fig. 16 Seventh horizontal section from the top. It passes through the 
upper portion of the entoderm and the secondary mesoblast (m). 
JOURNAL OF MORPHOLOGY, VOL. 26, No. 2 
