MONILIGASTER GRANDIS, A. G. B. 317 
is in an adult worm so arranged as to reduce the (body) cavity 
of Segment x1 to two sacs; one of these contains the ovaries 
aud nephridia of the segment, and into it the oviducts open 
internally (the oviducts are, as a matter of fact, mere modifica- 
tions of a portion of the wall of this segment) ; the other sac 
contains the portions of the dorsal vessel, the alimentary canal, 
and the ventral vessel, which belong properly to the segment. 
The portion of this septum which forms the latter of the above- 
mentioned sacs does not touch the body-wall at all; the portion 
forming the sac containing the ovaries, &c., joins the body- 
wall along a small portion of the ventral region only; else- 
where it is attached to the septum which follows, viz. x1-x11, 
The nerve-cord does not lie in any portion of its course in the 
cavity of Segment x1; there is a free passage through from 
Segment x to Segment x11. (See the arrow in fig. 27, and note 
also in this figure the arrangement of this septum in relation 
to the duct of the nephridium of this segment.) The cavity of 
Segment xt only passes forward to its proper limit as a cecal 
prolongation surrounding the nephridial duct. 
Septum xi-x11 is attached to the body-wall in the normal 
position, and is only peculiar in being prolonged backwards 
to form the wall of the receptaculum ovorum (figs. 17 
and 59), 
The remaining septa are normally attached ; those of the 
three or more segments following x1-x11 get pushed back by the 
receptaculum ovorum on each side, the number of septa thus 
displaced depending on the time of year, i.e. the state of the 
development of the receptaculum ovorum; but when this is 
fully developed it may rupture some of the septa; further, 
those septa in the neighbourhood of the gizzard become much 
displaced where they surround the alimentary canal, as they 
must be, considering that the gizzard region when extended 
occupies 35 mm., while the five segments containing it measure 
when contracted only about 5 mm. in length. 
The relation of the septum to the chief organs which run a 
longitudinal course from segment to segment is indicated in 
fig. 13, from which it will be seen that the septum is in actual 
