DEVELOPMENT AND ANATOMY OF SOME EARTHWORMS. 17 
any of the teloblasts except the ‘‘ mesoblasts” as specially 
enlarged as they are in Lumbricus. 
I gather from Bergh (‘Zeit. f. w. Zool.,’ Bd. 1, p. 523) that 
Wilson has, in a paper which I have unfortunately been unable 
to see, shown that “the outer setigerous glands arise from the 
lateral cell-cord,” and that he recognises a “ setiblast.”” My 
observations, which were originally made without any knowledge 
of the’previous literature, corroborate Wilson’s, but go further, 
as I show that all the setal matrices, however many there may 
be, arise on each side of the body as a cell-cord. My observations 
on the development of other organs are still very incomplete, 
but so far as they go they have led me to the conclusion that 
all the organs which express a metameric segmentation arise 
from the cords of cells which grow forwards in the germ bands. 
The mesoblastic bands give rise, I believe, to the muscles of 
the septa and ccelomic epithelium and blood-vessels only, while 
the muscles of the body-wall which do not exhibit metamerism 
arise in some other way. I find no evidence that they arise 
directly from epiblast, but a certain amount that they arise at 
an early stage from the primary mesoblasts, and perhaps also 
from the mesoblastic cords before these have become segmented, 
growing outwards in all directions, and not in that direction 
alone which is taken by the mesoblastic cords. Certain it is 
that at a time when the germ bands are still in their infancy 
muscles are to be found underlying the whole of the epiblast, 
Besides the muscles of the body-wall, the epidermis, and the 
alimentary tract, the only other organs which do not arise from 
the germ bands exhibit no metamerism in the embryo. The 
occurrence of such organs as the gizzard in such varying seg- 
ments in different worms would be explained if we can show 
that what segmentation the alimentary tract possesses has 
nothing to do with the metameric repetition of other organs. 
I have further, like Bergh, come to the conclusion that the 
nerve-cord arises from two distinct matrices, and that the 
ganglia are the only structures which arise from the neuro- 
blastic cords. The above theory will, I foresee, land us in 
great difficulties when we consider organisms other than worms, 
VOL. 36, parT 1.—NEW SER. B 
