402 WILSON. [Vot. III. 
surface and form the dorsal lip of the blastopore; at a later 
period they are overgrown by the ectoblast and thus come to lie 
between the ectoblast and entoblast in the median dorsal line. 
This account of their position and mode of origin holds true for 
Lumbricus communis and Lumbricus terrestris, but in Lumoricus 
fetidus, the form which I have most carefully studied, they 
appear to be wholly wanting (see p. 422). In this species the 
dorsal lip of the blastopore is formed by large entoblast cells 
covered dorsally by flattened cells of the ectoblast (Figs. 35, 46). 
As development proceeds the lateral areas of thickened ecto- 
blast extend forwards until they meet above the blastopore, the 
“ Schluckzellen”’ (in LZ. communts and L. terrestris) being thus 
covered and pushed somewhat backward. At a slightly later 
period these ectoblastic bands extend ventrally around the blas- 
topore until they meet and quite enclose it on the ventral side 
(Fig. 43). The thickened ectoblastic lips thus formed now grow 
into the blastopore to form the stomodzeum which is in this man- 
ner fully established very soon after the narrowing of the blasto- 
pore. The opening into the archenteron appears never to close, 
and even before the establishment of the stomodazeum the embryo 
begins to swallow the albumen in which it floats. 
The middle stratum of the germ-bands can first be distin- 
guished while the embryo is still nearly spherical, immediately 
after the establishment of the stomodzum. At this period 
close examination of the surface of the bands near their middle 
part shows some of the ectoblast cells to be arranged in distinct 
longitudinal rows, each one of which terminates posteriorly in 
a larger cell or teloblast (Figs. 47, 49; and Plate X1X.). Sec- 
tions at this stage show that the cells of these rows, and the 
teloblasts at their extremities, form a part of the general ecto- 
blast, though here and there they are overlapped by the adjoin- 
ing cells, and in some cases may be actually covered (Figs. 53, 
54, 66-68). In later stages the teloblasts and corresponding 
cell-rows gradually sink below the surface and thus give rise to 
a stratum of cells lying between the mesoblast and the outer 
ectoblast, but imbedded in, and clearly forming a part of, the 
latter (Figs. 70, 71, 72). Their precise mode of origin and 
ultimate fate are described further on. 
The germ-bands are now fully established, and their sub- 
sequent general development may be briefly sketched as follows: 
