558 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
the lateral border of the brain lobe. This canal represents what is 
later to become the glandular portion of the sense organ, although 
it is at first surrounded by ganglion cells (pi. 24, fig. 12). The 
body of the sense organ likewise extends back along the lateral face 
of the brain. 
The primitive position of the sense organ is thus seen to be imme¬ 
diately anterior and lateral to the anterior end of the brain, so that 
a transverse section through this region of the brain passes through 
the posterior part of the sense organ (pi. 24, fig. 11). This remains 
the permanent position in some species of the genus, as in G\ aus- 
traliensis , where the glandular canal extends posteriorly beside and 
even behind the brain. In G. agricola , however, the body of the 
sense organ remains of small size and comes to lie at some little 
distance in front of the anterior end of the brain. The opening of 
the ciliated tube on the exterior of the head in the adult is placed 
much farther forward relatively to the brain, and the tube itself is 
much more slender than is the case in the embryo. 
The change in the relation of these organs is accomplished by the 
growth of the connective, muscular, and glandular tissues in front 
of the brain, so that this organ, which lies so near the anterior end 
of the body in the embryo, is pushed far back from the tip of the 
snout in the adult worm. An elongation occurs also in the rhyn- 
chodaeum and in the cephalic glands. It is of particular interest to 
note that in many species of Hoplonemertea this primitive position 
of the sense organ corresponds so closely with the final position in 
the adult. 
Cephalic glands .— Early in the development of the embryo certain 
ectodermic cells at the anterior end of the body sink inward beneath 
the integument and by increase in both size and number give rise 
to the cephalic glands. The cells are at first of small size but later 
become distended with an enormous amount of deeply staining 
secretion, so that they are very conspicuous from an early period in 
all embryos (pi. 23, figs. 5, 6; pi. 24, figs. 10, 12, 13 ; pi. 25, fig. 19). 
They gradually migrate posteriorly, some of them passing behind 
the brain lobes, but remain connected with each other anteriorly 
and continue to discharge their secretions at the tip of the snout. 
A tubular invagination of the superficial epithelium on the snout 
forms a deep pit, into which the glands then pour their secretions. 
This pit grows back as far as the brain lobes and becomes lined 
