DEVELOPMENT AND ANATOMY OF SOME EARTHWORMS. 19 
secondary matrices is taking place, these being connected by 
the intermatricial band. This band disappears very early in 
Moniligaster, and in the anterior segments are seen inner and 
outer secondary matrices, as’ at s.m.?. and s.m.o. In the 
most anterior segment drawn, a seta (se¢.) is appearing in the 
inner secondary matrix. The embryo from which this figure 
is drawn has about fifty segments in front of those drawn, but 
it is not possible to count any segments behind those drawn, 
i, e. they are not distinguishable as segments in such a pre- 
paration ; longitudinal sections enable one to count them further 
back. 
Figs. 10—13 show the development of the secondary 
matrices in Moniligaster studied in sections. They are taken 
from a series cut transversely through a portion of an embryo 
of about the same age as fig. 9, and which had been flattened 
out in the same manner. They represent the matrices of four 
consecutive segments ; three or four sections are omitted between 
those figured. The upper part of each figure lies near the 
nerve-cord. They are drawn with a camera lucida to the same 
scale as figs. 1—7. Figs. 10 and 11 show primary matrices, 
that in fig. 11 projecting freely into the ccelom, while that in 
fig. 10 does not ; and in these segments there is quite clearly 
no other setal matrix on either side of the nerve-cord. In the 
next segment in front, the primary matrix has given rise to two 
secondary matrices on each side, those of one side being shown 
in fig. 12; four inches of the drawing have been cut out in the 
middle to place it upon the plate. In the next segment in 
front, the inner and outer secondary matrices are quite sepa- 
rated from one another; the inner one alone is figured. The 
epidermic thickening marked z is one of a series of such struc- 
tures with regard to which I can at present give no further 
information. I figure it to show that it is not a “ seta follicle.” 
Fig. 14 is a surface view of a secondary matrix, showing the 
development of the seta couple (set., set.) ; the coelomic epithe- 
lium shown allround is omitted from the surface of the matrix. 
Fig. 15 shows in a slightly older stage, from a longitudinal 
section, one of the setz of a couple. 
