142 JULIA WORTHINGTON. 
There are also large blood sinuses in this intra-dural space. 
The fibres of both inner and outer layers, throughout the 
greater part of the dura, are rather larger as a whole than 
those connecting the layers, and hold in their meshes the 
usual connective-tissue cells. ‘Toward the caudal end of the 
medulla, at the level of the anterior end of the plate of cartilage 
described above, the entire composition of the dura changes. 
The finer fibres and most of the small cells disappear, and 
are replaced by heavy, coarse, stiffly-curled fibres, packed 
closely in the two layers, and fairly closely in the intra-dural 
space, particularly on the ventral side. In the dorsal intra- 
dural space, they are farther apart, and enclose in their 
meshes numbers of large ovoid cells, not found elsewhere. 
These cells have a fine protoplasmic network, staining lightly 
in hematoxylin and alum carmine, and a small, deeper- 
staining nucleus containing a very distinct nucleolus, and 
several granules. 
Tue Bran. 
General Description.—The brain of Bdellostoma is 
about 10 mm. long. It is from 5 to 7 mm. wide through the 
fore end, and from 4 to 4°5 mm. wide through the hind end. 
The following table gives the external measurements of four 
brains. Of these, brain A is thatof B. Dombeyi, and B, 
C, and D belong to B. Forsteri. 
Length. A B Cc D 
mm. mm. mm, mm. 
Total length . : {lOO sols 9°95 10-0 
Olfactory lobes : oa" ilio 2°0 15 15 
Fore brain : : am (pene) 20 2°0 2°2 
*"T'ween brain (dorsal view) . 1:5 15 1°6 15 
Tween brain (ventral view) . 2°5 3°0 2°4 
Mid brain : , hy oie 2°0 20 2-0 
Cerebellum. . ee 15 15 16 
Medulla ‘ Siena o'0 o°0 eS) 
