DEVELOPMENT AND ANATOMY OF SOME EARTHWORMS. 15 
and are attached to the septa bounding these segments ante- 
riorly. The ciliated rosettes lie in the usual position. The 
prostates are long tubular-shaped glands, but remain in Seg- 
ment XVIII. 
The spermathece are elongated pyriform sacs with a small 
ceecum. 
The ovaries and oviducts lie in the usual positions. 
SETA. 
The setze which first develop are, in all the worms which I 
have studied, replaced by others in either all or in the greater 
number of the segments before the embryo leaves the capsule ; 
the replacement takes place in regular order from before back- 
wards, and if it has not taken place in the hindermost seg- 
ments before birth it does so shortly after. I speak of the 
setze which first develop as embryonic sete, and of the sete 
which replace them as permanent sete, although, of course, 
these may drop out and be again replaced later. The groups 
of cells from which the embryonic setz of any segment: de- 
velop I term secondary setal matrices. The secondary 
setal matrices develop from a primary setal matrix in 
each segment on each side of the body whether the complete 
number of setz in the segment is four on each side or a larger 
number, as in the Perichetide. 
Origin of the Primary Setal Matrices, 
To exemplify this I have taken figs. 1—8 from sections of 
an embryo of Mahbenus imperatrix. ‘The embryo was the 
same as that drawn in fig. 33, and was 7 mm. long when 
removed from the capsule. The sections were cut longitu- 
dinally through the tail end after it had been flattened out as 
in fig. 83. They are ‘006 mm. thick. They were drawn with 
a camera lucida and Zeiss F, oc. 3 (for figs. 1—6; oc. 2 for 
figs. 7, 8), and as drawn are, therefore, magnified about 1100 
diameters. The indentation marked z in figs. 1—8, due to a 
fold caused by the flattening, serves to mark the relative 
