186 GEORGE W. TANNREUTHER 
have a common opening on the dorsal side of the third 
segment. The funnel of the left occurs in the second and that 
of the right in the third segment. The posterior pair is found 
in the eighth segment. Each nephridium has a separate opening 
to the exterior on the dorsal side of the eighth segment. 
GROWTH 
The developing embryo does not increase appreciably in bulk 
until after the teloblasts are formed. Up to this period it is 
merely a division of the egg content into the various cell com- 
plexes. Even at this stage the increase in the long axis of the 
embryo is brought about by a decrease in the transverse diameter. 
Figures 50 and 55 show the transverse axis greater than the longi-. 
tudinal, while in figure 56 and 57 the longitudinal axis is greater, 
due more to a change in shape than to growth. The egg content 
is very plastic and when removed from the cocoon the egg mem- 
brane, in most cases, is not of sufficient tenacity to retain the 
embryo intact. The ten teloblasts are shown in figures 56 and 57. 
The first increase in length is due to the formation of the 
mesoblastic portion of the germ bands (text figs. 17-18). The 
neuroblastic and nephroblastic portions of the germ bands 
begin simultaneously after the meso-teloblasts have formed 
eight or ten cells (text figs. 15, 18 and fig. 58). Figures 58-71 
show the various stages in the formation of the germ bands. 
Figure 71 is about the last stage when the germ bands can be 
detected externally. A longitudinal section of figure 71 near 
the median axis shows a differentiation of the germ bands into 
their incipient organs (fig. 99). From this point of development, 
growth is very rapid, and the embryo begins to rotate on its 
transverse axis. The movement is produced by the action of 
cilia, which occur on the large ectodermal cells in the median 
ventral half of the anterior end of the embryo (figs. 96-99). 
These cilia disappear before hatching, but the cells from which 
they are produced persist as a part of the ectoderm. The an- 
terior and posterior ends are no longer in immediate contact, 
as in figure 71, but begin to overlap. The ends of the embryo 
