No. 3.] THE EMBRYOLOGY OF THE EARTHWORM. 413 
them the cesophageal commissures pass nearly vertically down- 
wards to the sub-cesophageal ganglion, which likewise lies in the 
third somite! (see p. 417). 
The stomodzeum of ZL. fetzdus differs remarkably from that of the other 
species studied. In Z. terrestris and L. communis the invaginated ectoblast 
is but slightly thickened and is directly continuous with the general ectoblast. 
In L. fetzdus, on the other hand, the ventral lip of the stomodzeum becomes 
expanded like a funnel, and greatly thickened, especially towards the sides, 
so as to form a swollen mass of elongated fusiform cells which in sagittal sec- 
tions (Fig. $2) is strikingly like a taste-bud. This mass (which seems to 
correspond to the ‘*‘ Mundwulst” of Crzodrzlus) is transversely elongated so 
as to form the entire ventral lip of the stomodzum. In some cases it is 
slightly bilobed, but usually is nearly uniform in thickness. The cells are 
attenuated towards their outer ends, and the peripheral ones are curved so as 
to bring the ends of all the cells together at the surface. Ventrally the cells 
of the stomodzal lip abut against those of the ventral ectoblast, from which 
they are separated by a very distinct line of demarcation. Inwardly they are 
also separated, though less markedly, from the cells of the narrow part of the 
stomodeum. The cells of the thickened lip are slightly granular, but not 
more so than those of the inner part of the stomodzum; their nuclei are 
large and conspicuous. In later stages the thickening gradually disappears 
and its cells appear to be converted into ordinary columnar epithelial cells like 
those forming the general wall of the stomodzum. 
Iam unable to say whether this larval structure is to be regarded as a 
glandular or a sensory apparatus. It suggests in its structure, position and 
mode of origin the paired larval sense-bulbs, or primary sense-organs of the 
lip found in the Hirudinea (see Whitman, No. 52, p. 159), which by fusion in 
the middle line would give rise to precisely such a thickened lip. Moreover, 
Hatschek figures (No. 18) the ‘“*Mundwulst” of Crzodrdlus as arising from 
completely separate foundations. On the other hand, it is difficult to un- 
derstand the use of so highly developed a sense-organ in but one species of 
Lumbricus, and its presence is so obviously correlated with the peculiar char- 
acter of the albumen in Z. fetzdus, that I am inclined to regard it as a larval 
digestive gland. It will be remembered that in this species the albumen is 
tough and jelly-like, differing markedly from the slimy, mucus-like albumen of 
other forms. It seems therefore not unlikely that the cells of the organ in 
question may pour forth a secretion to soften the albumen and thus facilitate 
its ingestion by the young embryo. 
In LZ. communis and terrestris there is no indication of this structure at any 
period. In both these species, however, peculiar deeply staining gland-like 
cells are found in the anterior part of the stomodzum (see Fig. 81), lying for 
the most part in its ventral wall, but also extending up on the sides, in some 
cases reaching the dorsal wall. These cells may perhaps be of the same na- 
1 This backward shifting of the cephalic ganglia is characteristic of many Oligo- 
cheta. See Vejdovsky, No. 44. 
