518 WILLIAM BATESON. 
Behind the lumen it has the appearance shown in fig. 78. 
The white matter does not enclose the upper part of the cord. 
Above it are a number of pyriform cells, probably ganglionic, 
whose tails project into the white matter. Central to these 
the cells are more or less irregularly grouped into strands 
enclosing spaces. The histology of this central part of the 
cord is very difficult, and I have not been able to determine 
how these spaces are filled. In B. minutus (v. fig. 67) they 
are so definite as to make it certain that they are not due to 
reagents. 
Among this loose tissue of the centre of the cord are remark- 
able stellate groups of cells (fig. 78, ste.) whose heads are thus 
placed radiating from a small lumen, which is generally 
sharply defined on three sides and usually irregularly bounded 
at some part of its margin. The nature of these stellate 
groups did not appear. They are commonest in the sides of 
the “ grey ” tracts, viz. at the points where the white matter 
is bent up (v. fig. 74, 6). It is possible that the spaces thus 
enclosed may in some indirect manner communicate with the 
neural tube. 
The histology of the cord is nearly the same in all the 
species. In B. Salmoneus and B. Brooksii, however, there 
is always a quantity of yellowish granules embedded in the 
central substance (on the analogy of Nemertines this substance 
may function like hemoglobin). The shape of the cord in 
section varies in the different forms and in different parts of 
its course (v. fig. 74). 
From the lower surface of the white matter of all species 
many fibres may be seen leaving the cord and losing them- 
selves among the subjacent muscular tissues. In B. Kowa- 
levskii alone no connection exists between the dorsal side of 
the cord and the skin. In B. minutus this is accomplished 
by three cords of skin substance. Their outsides are covered 
with a fibrous sheath (Spengel), and this is in connection with 
the fibrous layer of the skin. As Spengel has stated, these 
cords contain a more or less distinct lumen. I have not been 
able to trace this out upon the skin, though they occasionally 
