DEVELOPMENT AND ANATOMY OF SOME EARTHWORMS. 23 
but the sete themselves are magnified. It is very rare in the 
adults of this species to find young sete ready to replace old 
ones which drop out, and I believe that the sete shown in 
this figure were the “‘ permanent” sete formed in the embryo. 
I term them permanent setz in contradistinction to the em- 
bryonic setze which precede them. The permanent sete deve- 
lop at regular intervals from one another, except for the dorsal 
and ventral gaps, and a greater number are formed than occur 
in the adult, so that some drop out, leaving those which remain 
at irregular intervals from one another. The number of those 
that drop out appears to be nearly constant. 
The permanent setze begin to appear on either side of the 
dorsal and ventral median lines, one in the immediate neigh- 
bourhood of each embryonic seta (fig. 30); the last to appear 
are the most laterally placed ones. If 50 sete develop in the 
ring (the largest number I have found in this species) seta 1 
develops first, then seta 25 on each side, then in fairly regular 
order, 2, 24, 3, 23, and so on. They always develop first in 
the most anterior seta-bearing segment (11), and then very 
regularly backwards. They always begin to appear before the 
embryonic sete are visible in the most posterior segments. I 
give three examples: 
1. Embryo 25 mm. long, 160 segments counted, with a 
growing tail in which the segments could not be counted when 
mounted whole, embryonic setz visible down to Segment Lxv, 
but mere dots after xxx, and four pairs only present in the 
hindermost of the segments in which setz are already visible 
(say Lv to Lxv); the permanent sete are just beginning to 
develop, and are visible in Segments 11—V (see fig. 31). 
2. Embryo 30 mm. long, embryonic setz visible down to 
Segment ci11, the number of embryonic and permanent setz 
in the anterior segments are as under : 
